A discrete random variable takes on the values 0,1,2 and 3 with probabilities 1/8,1/4,1/8 and 1/2 respectively. Determine the pgf of the sum of two such random variables which are independent, stating any properties of the pgf you use.

The same type q comes up each year and I'm still unsure of how to tackle it? Any help would be much appreciated, test is on sat,