分式算数题已知1/a -1/b =3,求分式（2a+3ab-2b）/（a-ab-b)的值.

1/a-1/b=3,
(b-a)/ab=3
b-a=3ab
a-b=-3ab
(2a+3ab-2b)/(a-ab-b)
=[2(a-b)+3ab]/[(a-b)-ab]
=(-6ab+3ab)/(-3ab-ab)
=-3ab/(-4ab)
=3/4