The cash register deducts $2.50 from a $25 Coffee Café gift card for every medium coffee the customer buys. An equation is written to calculate the total amount on the gift card. What is the meaning of the y-intercept in the equation?
a) The change in the amount of money spent
b) The ending value on the gift card
c) The amount of money spent each visit
d) The initial value of the gift card