Brendon makes and sells greeting cards. He charges $5.00 for 2 cards, $7.50 for three cards, $12.50 for 5 cards, and $20.00 for 8 cards. Which equation shows the relationship between the number of cards, n, and the total cost, c?
a. c= 2/5 n b. c=0.4n c. c=2.5n d c=2.5 + 5
