Question 668204
let a = Abe's amt
let b = Ben's amt
:
 If Ben gives Abe four dollars, Abe will have three times as many dollars as Ben.
a + 4 = 3(b-4)
a + 4 = 3b - 12
a = 3b  -12 - 4
a = 3b - 16
:
If Abe gives Ben four dollars, they will have the same amount. 
a - 4 = b + 4 
a = b + 4 + 4
a = b + 8
:
Replace a with (b+8)  in the 1st equation
b + 8 = 3b - 16
8 + 16 = 3b - b
24 = 2b
b = $12 has Ben
then obviously
a = $20