1) 3/7 & -6/7 pls I need answers

Find an bif a = {3, 6, 9, 12) and b = {2, 4, 6, 8, 10).

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! )

Charlie tosses five coins. what is the probability that all five coins will land tails up.