Set up an equation to help you determine the amount of hours she works.
13.5(40) + 20.25x = 661.50
Multiple 13.5 and 40.
540 + 20.25x = 661.50
Subtract 540 from both sides to get x by itself.
20.25x = 121.5
Divide 20.25 off of both sides to get the amount of hours she worked after completing 40 hours.
x = 6
Now add 40 and 6 together, which is 46.
She worked 46 hours in that week.