Which sequence represents the function f(x)=7x−4, f(x)=7x−4, with a domain of natural numbers?
a. {3,10,17,24,…}
b. {4,11,18,25,…}
c. {4,−3,−10,−17,…}
d. {7,3,−1,−5,…}

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! )