A store sells gift cards in preset amounts. You can purchase gift cards for ​$20 or ​$30. You have spent ​$680 on gift cards. Write an equation in standard form to represent this situation. What are three combinations of gift cards you could have​ purchased?
Let x be the number of gift cards for ​$20​, and let y be the number of gift cards for ​$30. Write an equation in standard form to represent this situation