Sam bought 8 new basketball trading cards to add to his collection. The next day his dog ate half of

Sam bought 8 new basketball trading cards to add to his collection. The next day his dog ate half of his collection. There are now only 40 cards left. How many cards did Sam start with?

Let the starting about of cards be s.

Sam adds 8 new cards, so he has s + 8.

Then the dog ate half, so he's left with half. Sam is left with 40 cards:
(s + 8)/2 = 40

Cross multiply:
s + 8 = 80

Type s + 8 = 80 into the search engine, and we get s = 72