HELP ASAP PLEASE (20 points)
An open-topped box is to be created from a 100 cm by 80 cm piece of cardboard by cutting out a square of side length x from each corner.

a) Write an expression for the volume of the box in terms of x.
b) Write an expression for the surface area of the open-topped box in terms of x.
c) Write a simplified expression of the ratio of the volume of the box to the surface area.
d) Refer to your answer in part (c). State the restrictions on x