8 would be the coefficient :)
The average rate of change of a function f(x) over an interval (a, b) is given by

Therefore, given a function, f(x), over an interval (2, 9), the average rate of change of the function can be found using the expression
So in a cube, the width, length, and height are the same. Therefore, you have to find the cube root of 15.625 which is 2.5 and so the side length is 2.5