The slope is 3.
10 - 7 = 3
4 - 3 = 1
Final step is to do 3 divided by 1 and you get 3.
You haven't told us whether the rectangular prism is the size of a pack of gum or more like the size of a cruise ship.
Whatever size it is, here's the number of centimeter squares you need to cover the whole outside of it:
(2 x length x width) + (2 x length x height) + (2 x width x height)
with all measurements made in centimeters.
With a square, all you need to do to find the length of one side is to divide the perimeter by 4. If it is the area you are calculating, then you need to find the square root. For that equation the answer is 24.