The inequality is:
18 > 30 - 1.99x
because >18 is the end balance (y value), 30 is the original balance/starting value (y-intercept), and -1.99 is the amount the balance changes (slope) per every song download/day (x).
To solve the inequality, first subtract 30 from both sides, to get:
-12 > -1.99x
Then divide both sides by -1.99, but since you’re dividing by a negative, make sure to switch the inequality sign as well. This results in:
~6 < x
That means the gift card will still have a balance of more than 18 for a little more than 6 days.
This might be wrong so sorry if it is… my math and logic seems to make sense tho