Look at the base of your box to solve for x.
The base is a rectangle and has 2 sides that are 3x+2 and 2 sides that are 2x-2. If you add the lengths of all 4 sides, you get a perimeter of 60.
So, 3x + 2 + 3x + 2 + 2x - 2 + 2x - 2 = 60
Combining like terms leaves you with 10x = 60
Therefore x = 6. Which is the height of your box.
To find the volume, find the area of the base and multiply it by the height.
(3x + 2)(2x - 2)(x) = volume
substituting 6 for x, we get
(18 + 2)(12 - 2)(6)
(20)(10)(6) = 1200cm3