your bank account has $-15 in it. You deposit $5 per day
After you've made all your deposits you withdraw two dollars a day until your account balance is $0.
how many days will you withdraw $2 ?
Assuming that you deposited for 5 days like the last problem
5*5 = 25
25 + 15 = 40
So you have to keep withdrawing 2 from 40 until it is 0
How many times does 2 fit into 40?
40 / 2 = 20
20 days