Question 64144
a^2 - b^3(a - b) [substitute:  a = 1/3 and b = - 1/2]
(1/3)^2 - (-1/2)^3((1/3) - (-1/2)) [simplify]
(1/9)+(1/8)(1/3+1/2)
(1/9)+(1/8)(2+3/6)
1/9+1/8(5/6)

1/9+5/48
(48+45)/432 = 31/144