Probably y = 8x. 56 = 8(7), so that works. Without more data, I couldn't say if it could be something else, so that's what I go with.
Short Answer: 560 cm squared
Long Answer:
You can get the volume of a rectangular prism by multiplying the height, width, and length together.
We need an image to be able to answer this question
So (f-g)(x) = 3x2 + x, so when x = 2, the function is 14
