David's savings was 75% as much as Alan. After Alan saved another $40 and David saved another $20, David's savings became 5/8 as much as Alan. Find David's savings at first.
D = .75A → D / .75 = A → D / (3/4) = A → (4/3) D = A (1)
(D + 20) = (5/8) ( A + 40) (2)
Sub ( 1) into (2)
D + 20 = (5/8) [ (4/3)D + 40]
D + 20 = (20/24)D + (5/8) (40)
D + 20 = (5/6)D + 25
D - (5/6)D = 25 -20
(1/6)D = 5
D = 5 ( 6/1) = 30
David had $30 at first
