Answer
Find out the how much did Sheila have at first .
To proof
Let us assume that the original amount of money be x .
As given
Sheila went shopping and spent $120 on a coat.
Than
money sheila has = x - 120


Than the equation becomes

L.C.M of (5,3) = 15

solving
600 +13x = 15x
600 = 15x - 13x
600 = 2x

x = $300
The shelia have money be $300 .
Hence proved