First of all, we need to write a function or equation that describes the behavior of Choy's lunch account at school.
if x will be the numbers of days, y will be the amount of money in his account, then=
Now, after two weeks = 5*2 = 10 days, we need to find y(10) replacing x= 10 in the previous equation, like this:
Finally, the balance on his account is a debt of 5 dollars.