Ahmad has $1380 more than Ben at first. After each of them spent $640, Ahmad had 5 times as much money as Ben. How much did Ben have at first?
+36915 Initially
a = 1380 + b
then
(a-640) = 5 (b - 640) sub in the red equation
(1380+b) - 640 = 5b - 3200
b = 985
