What was her two mistakes in this problem

We must first determine the shape of a rectangular prisms _ a0 to find area of the prism

Asmall business produces and sells balls. the fixed costs are $20 and each ball costs $4.32 to produce. each ball sells for $8.32. write the equations for the total cost, c, and the revenue, r, then use the graphing method to determine how many balls must be sold to break even.

Ithink i know it but i want to be sure so can you me out ?