Function rule: a = 20w + 115
Slope: 20
Initial value: 115
------------------------------------------
We start with $115 in the account. This is the initial value. Each week we add on $20.
So we add $20 for 1 week
We add 2*20 = $40 for 2 weeks
We add 3*20 = $60 for 3 weeks
etc etc
In general, we add 20*w dollars for w weeks onto 115 to get a = 20w+115
The slope is 20 because this is the rate of change, ie how fast the account grows. It grows 20 dollars per week.