Question 1008645
Call Ama's age NOW, a.  Her sister's age NOW will be s.  Then we have
a = (2/3)s
a - 4 = (1/2)(s - 4)
Substitute the first into the second equation and get
(2/3)s - 4 = (1/2)(s - 4)
Multiply by 6 to clear fractions and get
4s - 24 = 3(s - 4)
4s - 24 = 3s - 12
Subtract 3s and add 24 and get
s = 12
a = (2/3)(12) = 8
Ama is 8, the sister is 12.