To answer this problem, you will need to turn (a/z) and (y/a) into variables with a common denominator, much like with adding any fraction.
In this case, the common denominator will by a multiplication of the two existing denominators, z and a, because there is no way of knowing what each equals as a number.
To make the first fraction have az as its denominator, you need to multiply (a/z) by a which gives you (a^2)/(az)
SImilar to the first, you will multiply (y/a) by z to get az as the denominator. This would look like (yz)/(az)
Adding both variables (a^2)/(az) + (yz)/(az) will allow you to find your answer.
If you have any further questions on this or other problems, I would be more than happy to help.