Help, brainlest if best explained

Including 6% sales tax, an inn charges $135.68 per night. find the inns nightly cost

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! )

Find the rate of change for the situation.you run 7 miles in one hour and 21 miles in three hours.