Homework Guidance

I am working on some homework and I am trying to encrypt a file without using a passphrase. I have tried using RSA public and private keys however the file was far to large ( 10MB ) to be successful. i have tried a openssl enc -aes-256-cbc -salt -in file.txt \ -out file.enc -pass pass:mySillyPassword but there is no out put file that i can see and when i try the decryption it doesnt work.

my homework question is this Measure the time used for encrypting and decrypting the file without typing the passphrase. so i first have to figure out how to encrypt without a passphrase. the time thing is easy and i have that working all ready