At first, Xavier, Tommy and Ben had the same amount of money. After Ben spent some of his money, Xavier spent ³₅ of his money and Tommy spent ³₄ of his money, Xavier had $57 more than Tommy. In the end, the total amount of money the three boys had left was $315. How much money did Ben spend?

	Xavier	Tommy	Ben	Total
Before	5x4 =  20 u	4x5 = 20 u	20 u
Change	- 3x4 = - 12 u	- 3x5 = - 15 u	- ?
After	2x4 = 8 u	1x5 = 5 u		$315

The amount that Xavier and Tommy each had at first is the same.  Make the amount that they each had the same.  LCM of 5 and 4 is 20.

Amount that Xavier had more than Tommy in the end
= 8 u - 5 u
= 3 u

3 u = 57

1 u = 57 ÷ 3 = 19

Amount that Xavier and Tommy had in the end
= 8 u + 5 u
= 13 u
= 13 x 19
= $247

Amount that Ben had in the end
= 315 - 247
= $68

Amount that Ben had at first
= 20 u
= 20 x 19
= $380

Amount that Ben spent
= 380 - 68
= $312

Answer(s): $312