Renata wins a $20 gift card to an online music site. After Renata purchases 16 songs, the gift card has a remaining balance of $0. Which equation represents the relationship between y, the remaining balance on Renata’s gift card, and x, the number of songs purchased?

4x + 5y = –100
5x + 4y = 80
4x + 5y = 16
5x + 4y = 20