Jack’s lunch at a restaurant costs $13.00, without tax. He leaves the waiter a 17% tip of the cost of the lunch. What is the tip money Jack should leave?

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! )