18=a over 2 how do you solve that as a one step

Plz which expression is equivalent to the expression below?

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.

Use the given information to determine the exact trigonometric value.