Let <em>x</em> be the number of pearls in Chang's collection. Let <em>y</em> be the number of pearls in Cal's collection.<em />
Chang has 3 more than Cal, so <em>x</em> = <em>y</em> + 3. Adding both collections would be <em /><em>x</em> + <em /><em>y.</em> It's easier to have an expression in one variable, so we will substitute what we had written about Chang in for <em>x</em>. (<em>y</em> + 3) + <em>y</em> = 2<em>y</em> + 3.