Fred bought 5 new baseball trading cards to add to his collection. the next day his dog ate half of his collection. there are now only 42 cards left. how many cards did Fred start with?

42 cards is after his dog ate half, so before that would be 42 * 2 = 84.

Even before that, he bought 5 new baseball cards, so add that to the 84 cards and you have 84 + 5 = 89.

Fred started out with 89 baseball cards.