You don’t know how long or how much she got paid an hour on Monday. All you know is:
h = total number of hours she babysat on Monday, and she made $85.
Let r = the rate she got paid per hour on Monday, then rh = 85, and then r = 85/h
On Wednesday she babysat 8 hours at the same rate of 85/h and got an additional $12
The expression for how much she made on Wednesday is: 8(85/h) + 12