Starts at 100, so 100 is b in the equation y = mx + b
Since 6 is a constant addition addition through a period of time, it is the slope, or m, so we have y = 6x + 100, where y equals the money in john's account
We are given that it's 220, so y = 220.
220 = 6x + 100
220 - 100 = 6x + 100 - 100
120 = 6x
120/6 = 6x/6
20 = x
x = 20, so after 20 weeks John has 220 dollars.
