With #5 and #8! i don’t really know all of the info to find the volume! (composite figures)

It looks like you're doing good with breaking-down the composite into digestible pieces. So, don't stress too much!

Keep in mind that the area for a 3D shape is Bh, where "B" is the area of a face & "h" is the height.

#5
Shape A is 3X4X9.
First, calculate the area of a face:

9X4= 36

Multiply by height:

36X3= 108

The process is the same with shape B.
3X4X8
Calculate area of face:

8X4= 32

Multiply by height:

32X3= 96

Now you add both areas:

108+96= 204 cubic feet

I think you're doing pretty good, just don't over think things too much. Try #8 with the similar process seen here. Just comment if you get stuck.

Hope this helps!

How many desks and whats the price?