mark takes a 40 question test for which he receives 2.5 for each correct answer and losses 1 point for each wrong answer. If mark answers all the questions and gets a grade of 65% of the test, what percent of the questions did he answer correctly?

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! )