Think of it like this. Ship ONE has FIVE coins, and ship TWO has ONE chest and TWO coins. Every chest is ONE X. your equation would go like this.
X+2=5 Your first move would be to subtract TWO from each side, so then X can be by itself. You would get, X=3. And like I said above, every chest would be X. Your answer would be, Every chest has 3 coins.