Hiro and lisa are photographers. They take pictures for seniors for high school yearbooks. They charge a standard fee for taking pictures.Theres also a charge for each set of prints ordered. So the number of sets of prints determines the total cost .
set of prints (s) Total cost
0 $15
1 $18
2 $21
3 $24
let s stand for the sets of prints ordered. write the rule that describes a students total cost

Question

Hiro and lisa are photographers. They take pictures for seniors for high school yearbooks. They charge a standard fee for taking pictures.Theres also a charge for each set of prints ordered. So the number of sets of prints determines the total cost . 
set of prints (s)       Total cost 
                   0                $15
                   1              $18
                   2                $21
                   3               $24
let s stand for the sets of prints ordered. write the rule that describes a students total cost