What is the proportional numbers of 26/13

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.

Ineed with math stuff it involves graphs

Determine domain and range, largest open interval, and intervals which function is continuous.