Chang and Cal both collect pearls. Chang has three more pearls in her collection than Cal. Write an expression to represent the total number of pearls in both collections.

Let x be the number of pearls in Chang's collection. Let y be the number of pearls in Cal's collection.

Chang has 3 more than Cal, so x = y + 3.

Adding both collections would be x + y. It's easier to have an expression in one variable, so we will substitute what we had written about Chang in for x.

(y + 3) + y = 2y + 3.