Unable to umount or close external hdd

Ubuntu....auto-mounts

6TB HDD w/ 4 (?) partitions
1... sda1
2... sda2
3... sda3
4... sda4
ALL MOUNT POINTS START WITH "/MEDIA"

UNMOUNT:
Not sure how many partitions open.

"Sudo umount /dev/mapper"
----- says "/dev/mapper" not mounted

"Sudo umount /dev/mapper /unknown.name"
----- ----- says " no mount pt specified"

-------------------------------------
CLOSE: "Sudo cryptsetup luksClose name"
---- "Device X is not active"

I have forgotten most basic commands for linux

**** I can not access all partitions right now.

**** I need to umount / close so i can mount read only****

WHAT COMMANDS DO I TYPE IN TO DO THIS?


Thx

UPDATE 1:
I can unmount from partition 1 by right clicking on hdd icon, but it will only unmount 1st partition.

All partitions say "crypt" "luks" and all 3 mounted to media.

UPDATE 2:
Was able to unmount 3 partitions from ghe icon, with 1 still mounted to media. The icon disappeared. When i try to close, tells me device not active.

I'm trying to mount using "sudo mount /dev/mapper/name /mnt -o ro"
------ says: special device /dev/mapper/name does not exist.