(x^2-y^2)/6*12/(x-y). The easy part is that the denominator 6 divides into the numerator 12. Break down x^2-y^2 into factors: (x-y)(x+y). The denominator (x-y) divides and cancels out (x-y) in the numerator. What are we left with? (x+y)*2=2(x+y). Now, that wasn't so bad, was it? Note: when dividing by the common factor (x-y) it has to be assumed that x is not equal to y, otherwise we would be dividing by zero , which is a no-no.