Final answer:
The equation that will determine the amount of money the student will have left after d days is m = 15 - 2.20d.
Step-by-step explanation:
The equation that will determine the amount of money the student will have left after d days is m = 15 - 2.20d. This equation represents the student's initial amount of money ($15.00) minus the cost of the plate lunch ($2.20) multiplied by the number of days (d) that the student has been purchasing the plate lunch.