Aaron had 3/5 as much money as Brent at first. After receiving $12 each, the ratio of Aaron's money to Brent's money is 3:4. How much money did Brent have at first?
A = (3/5)B
A + 12 : B + 12 = 3 : 4
(3/5)B + 12 : B + 12 = 3 : 4
[(3/5)B + 12 ] 3
___________ = ___ cross-multiply
[ B + 12 ] 4
4 [ (3/5)B + 12 ] = 3 [ B + 12 ]
(12/5)B + 48 = 3B + 36
48 - 36 = 3B - (12/5)B
12 = (3/5)B
12 (5/3) = B = $20 = what Brent had at first
