65.
(a^2 + y^2)/(ay - y^2) - 20/(a - y) = (a^2 + y^2)/(y(a - y)) - 20/(a - y) = (a^2 + y^2)/(y(a - y)) - 20y/(y(a - y)) = (a^2 + y^2 - 20y)/(y(a - y))
74.
(a + b)/(a - b) - (a+b)/a = (a+b) * (1/(a-b) - 1/a) = (a+b) * (a/(a(a-b)) - (a-b)/(a(a-b))) = (a+b) * ((a - (a-b))/(a(a-b))) = (a+b) *b/(a(a-b)))