(a^2-b^2)/ab - (ab-b^2)/(ab- a^2)
#Using special product
= (a+b)(a-b)/ab - (ab-b^2)/(ab- a^2)
#Removing out a and b common
= (a+b)(a-b)/ab - b(a-b)/a(b-a)
#LCM of both denominators i.e. ab and a(b-a) is ab(b-a)
#Hence we multiply first equation by (b-a) and second equation by b
= (a+b)(a-b)(b-a)/ab(b-a) - b^2(a-b)/ab(b-a)
#Taking the denominator common
= [(a+b)(a-b)(b-a) - b^2(a-b)]/ab(b-a)
#Taking (b-a) common in the numerator
=[(b-a)(a^2-b^2-b^2)]/ab(b-a)
#Cancelling out (b-a) from numerator and denominator
=a^2 - 2 b^2 / ab
Hence B is the answer.