Question

a/a-3b*(3/a-1/b)   (деление в дробях)

Answer 1

3/a-1/b=(3b-a)/ab

a/(a-3b) * (3b-a)/ab=
a(3b-a)/(a-3b)ab=
-a(a-3b)/(a-3b)ab=
-a/ab=
- b