19) Jason received an Amazon gift card for his birthday. After he buys a song, the card's value is $17.21. After he purchases a second song, the card is worth $14.42. Jason downloads one more song and has $11.63 left on the card. i) Write an equation to define a as the amount of money left on the gift card after n purchases. ii) Jason plans to download a song every Tuesday moming. How many weeks in a row can he buy a song before the gift card runs out?​