Kathy went shopping with a certain amount of money. She spent 1/4 of it on shoes, 1/5 of it on lunch and 78 of it on cloths. She had 21 left. How much money did she have at first.
Let x = original sum
This is assuming that the 1/5 was of the original sum rather than after the 1/4 was spent.
x - .25x - .2x - 78 = 21
Solve for x.