*5.5w - 3.25 = 35.25
The 5.5w part shows that its $5.50 times each window. The -3.25 is because he deducted 3.25 from the total. And then you have the price that he got on the other side.
Here's the work to find the windows in case you want it:
5.5w-3.25=35.25
5.5w=38.50
w=7
He washed 7 windows