LaTeX: how to have this kind of indentation? (sorry for the vague title)

I have numbered book exercises to solve, and write their answer in LaTeX. I would like to write them with the kind of indentation the book uses. But i was not able to find that.

See these two pictures:

1. Exercises in the book, where the numbers are to the left of an imaginary margin for their text: http://imgbox.com/e4OtbWyT

2. What i was able to do, after a good amount of time playing with sections, subsections, paragraphs and one or two more commands. I found that subparagraphs are indented from where the paragraphs start, but when their are long enough, they continue where the indentation of the parent paragraph began. I reached this: http://imgbox.com/ItlxDls7

The important parts, in a way that works, of what i used for the second image, readable here:

Code:\documentclass[12pt]{article}
\usepackage{amssymb}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[portuguese]{babel}
\usepackage{hyphenat}
\hyphenation{mate-mitica recu-perar}
%-------------------------------------

\begin{document}
\pagestyle{empty}

\paragraph{\textbf{3.1.} Aa aa aa aaaaa
aaaaaaaa aaaaaaaaaaaaaa aaaaaaaaa aaaaaaaaaaa
aaaaaaaaa aaaaaaaaaaa aaa aaaaa aaaaaaaa
aaaaaaaaaaa aaaaaaaaaa aaaaaaaaaa aaaaaaaaa.}

\paragraph{\textbf{3.2.} Aaaaaaaa aaaaaa
aaaaaaa aaaaaaa aaaaaaaa aa a aaaaaaaaa aaaaa
aaaaaaaa a aaaa aaa aaaaaa aaaaaaaaaa.}
% textbf instead of itemize to get the ()
\subparagraph{\textbf{(a)} Bbbb bbbb bbbb
bbbbbbb bbbbbbbbbb bbbbbbbb bbb bb bb bbbb bb
$\pi$.}
\subparagraph{\textbf{(b)} Aaaa \textit{A},
\textit{B}, \textit{C} aaa aaaa aaaaaaa
aaaaaaaaaa aaaaaa aaaaaaaa aaaaaaaaaa aaaaaa
aaaaaaaaaa aaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaa
aaaaaa aaaaaa aaa aaaaaa aaaaa aaaa.}
\subparagraph{\textbf{(c)} Aaa aaaaaa aaaaa.}
\subparagraph{\textbf{(d)} Ccccccc cccccc ccc
cccccccccccc cccccccccccc ccccccc ccccccc ccccccc
ccccccccc cccccc cc ccc c c ccccccc.}

\paragraph{\textbf{10.3.} Aaaaa aaaaaaaaa
aaaaaaaaa aaaaaaaa aaaaaaa aaaaaaaa\textit{ABC}
aaaaaaaaaaa aaaaaaaaa aaaaaaaaa aaaaaaaaaa
aaaaaaaa aaaa aaa aaaa ldaksja ldjalkja d
lkasdj lakjd laks lkdasjldkasj uhelkjda lk
adslk jklasd jr.}

\end{document}The above code, without the artificial line breaks for readability:

Code:\documentclass[12pt]{article}
\usepackage{amssymb}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage[portuguese]{babel}
\usepackage{hyphenat}
\hyphenation{mate-mitica recu-perar}
%-------------------------------------

\begin{document}
\pagestyle{empty}

\paragraph{\textbf{3.1.} Aa aa aa aaaaa aaaaaaaa aaaaaaaaaaaaaa aaaaaaaaa aaaaaaaaaaa aaaaaaaaa aaaaaaaaaaa aaa aaaaa aaaaaaaa aaaaaaaaaaa aaaaaaaaaa aaaaaaaaaa aaaaaaaaa.}

\paragraph{\textbf{3.2.} Aaaaaaaa aaaaaaaaaaaaa aaaaaaa aaaaaaaa aa a aaaaaaaaa aaaaaaaaaaaaa a aaaa aaa aaaaaa aaaaaaaaaa.}
% textbf instead of itemize to get the ()
\subparagraph{\textbf{(a)} Bbbb bbbb bbbbbbbbbbb bbbbbbbbbb bbbbbbbb bbb bb bb bbbb bb $\pi$.}
\subparagraph{\textbf{(b)} Aaaa \textit{A}, \textit{B}, \textit{C} aaa aaaa aaaaaaa aaaaaaaaaa aaaaaa aaaaaaaa aaaaaaaaaa aaaaaaaaaaaaaaaa aaaaaaaaaaa aaaaaaaaaaaaaa aaaaaaaaaaaaa aaaaaa aaa aaaaaa aaaaa aaaa.}
\subparagraph{\textbf{(c)} Aaa aaaaaa aaaaa.}
\subparagraph{\textbf{(d)} Ccccccc cccccc ccc cccccccccccc cccccccccccc ccccccc ccccccc ccccccc ccccccccc cccccc cc ccc c c ccccccc.}

\paragraph{\textbf{10.3.} Aaaaa aaaaaaaaa aaaaaaaaa aaaaaaaa aaaaaaa aaaaaaaa\textit{ABC} aaaaaaaaaaa aaaaaaaaa aaaaaaaaa aaaaaaaaaa aaaaaaaa aaaa aaa aaaa ldaksja ldjalkja d lkasdj lakjd laks lkdasjldkasj uhelkjda lk adslk jklasd jr.}

\end{document}

In my latex code, it is important to note that:

- have each exercise number, for each answer, indented like in the book

- the section/subsection/list numbers i used where completely manual (i could not find another way to do them, although i tried)