Since he bought a few of each length. The only combination that works is when he bought 5 of the 4 ft long board so 4×5=20. Than he bought 3 of the 5ft boards 3×5=15. 20+15=35 ft worth of boards.
It's 5 over 9 because you start off with 10 cards (6 roses 4 daisies) then you pick a rose. Then it become's 5 over 9 since there are only 5 roses left and 9 total cards left.
