Your question is Window Cleaner Estimation. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Imagine you were a window cleaner that had been hired to clean all the windows in a city. How would you go about estimating the amount of work you would need to do and so how much to charge the city?