Which set of ordered pairs does not represent a function?
a. {(-3,-8), (-1,-6), (-2,5), (0,7)
b. {(7.0), (4, -1).(-6,5), (-8,0)
c. {46), (5,-7), (7,9), (8,-10)}
d. {(2,5), (3, 8), (4, 11), (2, -1)}​

I'm at a bookstore with $\$35$ in my pocket and a $20\%$-off coupon. what is the cost of the most expensive book i can buy with my money and the coupon? (assume that there are books of every possible price in the bookstore. it's a large bookstore! )