your bank account has -$-15 in it. You deposit $5 per day
How much money is in your account after 5 days.
Assuming you said $15 dollars
You deposit 5 per day, for 5 days.
So 5 * 5 = 25
You also started with 15
So 25 + 15 = 40
This can be modeled with y = mx + b
y = 5x + 15
With y = money
x = days