Marcus and Kevin had the same number of stamps at first. Marcus gave 1/4 of his stamps away and Kevin gave 1/3 of his stamps away. In the end, Kevin had 15 stamps fewer than Marcus. How many stamps did Marcus give away?
At first, they had the same amount. I will call this x.
Marcus now has 3/4 *x, and Kevin has 2/3 *x.
Marcus has 15 more than kevin, so I can list this as 3/4 *x=2/3 *x +15
Marcus gave away 1/4, so I multiply 180 and 1/4, which gets me 45.
Marcus gave away 45 Stamps.