In a cafeteria, 3 coffees and 4 donuts cost $10.05. In the same cafeteria, 5 coffees and 7 donuts cost $17.15. Also whats make you say your answer?

The variables are

c = cost of a coffee

d = cost of a donut

——————

Translating into equations:3 coffees and 4 donuts cost $10.05

3c + 4d = 10.055 coffees and 7 donuts cost $17.15

5c + 7d = 17.15

What is the question?