Marquise had 77 baseball cards he traded off 3 per day to get some extra food how many days did he conduct these trades if he only has 14 cards left

So he had 77 total. He gave away 3 per day (3 * # days). And has 14 left.

77-3d= 14
+3d on both sides
77=14+3d
Subtract 14 from both sides
63=3d
Divide both sides by 3
21=d

So in 21 days, he will have 14 cards left.

Check work:
77-3d=14
77-3(21)= 14
77-63= 14
14= 14

Hope this helps!! :)