Begin by switching the - to a plus. Switch the x and y in the second denominator.
5x^2 2x^2
===== + ======
6x - 6y 3x - 3y
Pull out the common factors in both denominators. Use the distributive property.
5x^2 2x^2
===== + ======
6(x - y) 3(x - y)
Multiply both the numerator and denominator by 2 on the left had fraction.
5x^2 2*2x^2
===== + ======
6(x - y) 2*3(x - y)
5x^2 4x^2
===== + ======
6(x - y) 6(x - y)
Put both numerators over a common denominator. Notice that the + sign shifts up. It shifts up because both fractions have been changed to a common denominator.
5x^2 + 4x^2
===================
6(x - y)
Combine the two numerators since they are of the same power.
The greatest common factor is the largest positive integer that divides evenly into all numbers with zero remainder. The largest number that goes into 12 and 8 is 4.