Need help with financial algebra

Answer: [tex]c(x) =\left \{ {{18\qquad 0<x\leq 3} \atop {6.5x+18\quad x>3}} \right.[/tex]
Step-by-step explanation:
The first equation is c(x) = 18 when x is between 0 and 3 (including 3).
The second equation is c(x) = 6.5x + 18 when x is greater than 3