Which algebraic equation correctly represents this statement? The square of the product of 4 and a number is the sum of the number and 15.

1. (4x)^2 = x + 15x
2. 4x^2 = x + 15
3. 2(4x) = x + 15
4.(4x)^2 = x + 15

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! )