Shelby, allen, and denise printed their digital photos. each requested the same size prints. shelby paid $2.70 for 5 prints. allen paid $3.24 for 11 prints. denise paid $4.05 for 20 prints

Person:    Number of prints      Total Cost
Shelby             5                               2.70
Allen               11                              3.24
Denise            20                             4.05

To solve for the variable cost:
11 - 5 = 6
3.24 - 2.70 = 0.54
0.54 / 6 = 0.09 per print

To solve for the fixed cost
0.09 x 5 = 0.45
2.70 - 0.45 = 2.25 

y = 2.25 + 0.09x

y = 2.25 + 0.09(5) = 2.25 + 0.45 = 2.70
y = 2.25 + 0.09(11) = 2.25 + 0.99 = 3.24
y = 2.25 + 0.09(20) = 2.25 + 1.8 = 4.05