Answer:
We know w is Westside and each hour costs $98, so we can say that:
98w
is the cost for Westside hours.
We don't know the number of Pinewood hours, but we know she is taking 20 combined credit hours, and w hours at Westside. So, we can say the Pinewood hours are 20-w.
Each hour at Pinewood is $115, so:
115(20-w)
Add the 2 expressions:
98w+115(20-w)
That is the expression for the total amount.