Oscar, Sean, Zeph and Justin went shopping with a total of $731. After shopping, they had a total of $108 left. Sean spent $90. The amount Zeph spent was ²₇ the amount spent by Oscar. The total amount spent by Oscar and Sean was $303 less than the total amount spent by Zeph and Justin. How much did Oscar and Justin spend altogether?

	Oscar	Sean	Zeph	Justin	Total
Before					$731
Change	- 7 u	- $90	- 2 u	- ?	- $623
After					$108

Total amount that Oscar, Sean, Zeph and Justin spent
= 731 - 108
= $623

Total amount that Oscar and Sean spent
= 7 u + 90

Total amount that Zeph and Justin spent
= 7 u + 90 + 303
= 7 u + 393 

Total amount that Oscar, Sean, Zeph and Justin spent
= 7 u + 90 + 7 u + 393
= 14 u + 483 

14 u + 483 = 623
14 u = 623 - 483
14 u = 140 

1 u = 140 ÷ 14 = 10

Total amount that Sean and Zeph spent
= 2 u + 90
= 2 x 10 + 90
= 20 + 90
= $110

Total amount that Oscar and Justin spent
= 623 - 110
= $513

Answer(s): $513