Given 1 / A-1 / b = 1 / 3, find (- 3A + 4AB + 3b) / (2a-3ab-2b)

1/a-1/b=1/3
(b-a)/ab=1/3
b-a=ab/3
a-b=-ab/3
The original formula = [3 (B-A) + 4AB] / [2 (a-b) - 3AB]
=[3(ab/3)+4ab]/[2(-ab/3)-3ab]
=5ab/(-11ab/3)
=-15/11