I need help figuring this out

mark and don are planning to sell each of their marble collections at a garage sale. If don has 5 more than 3 times the number of marbles mark has, how many does each boy have to sell if the total number of marbles is 81?

Ben starts walking along a path at 3 mi/h. One and a half hours after Ben leaves, his sister Amanda begins jogging along the same path at 7 mi/h. How long (in hours) will it be before Amanda catches up to Ben? Enter the exact answer. Hint: The distance formula is that distance = rate * time, so for example in one and a half hours, Ben has walked 3 * 1.5 miles. Amanda catches up to Ben in Number hours