Answer:
A. The original value of the gift card is 75 dollars, which is the y-intercept of the function.
B. The student spent 2.5 dollars each day at the coffee shop, which is the coefficient of n in the function.
C. After 20 days, the remaining value of the gift card is -2.5 * 20 + 75 = 25 dollars.
D. To find the total number of days until the gift card was used up, we need to find when f(n) = 0. Setting the function equal to 0 and solving for n, we get: 0 = -2.5n + 75, so n = (75)/(-2.5) = 30 days.