4) b/6a; 4a + 3b^2/18ab; x/9b
b/6a = [ b.(3b) ] / [6a.(3b) ] = 3b^2 / 18ab
x/9b = 2a.x / (2a.9b) = 2ax / 18ab
5) x/4a; 6a - 5bx/20ab; a -1/10b
x/4a = (x.5b) / (4a.5b) = 5bx/20ab
(a - 1)/10b = [(a - 1).2a] / (10b.2a) = (2a^2 - 2a) / 20ab
6) 5/3; 5x - 1/ 3(x+1)
5/3 = [5.(x+1)] / [3.(x+1)] = (5a + 5) / 3.(x+1)