There are 16 windows on the first floor.
Thus, the number of windows on the first floor is equal to
Given that there are 9 windows on the third floor, we set
There are thus 18 windows on the second floor, but there are two fewer on the first floor. Therefore the first floor has 16 windows.
We have to define a variable first to be able to make an equation.
The first floor has the smallest number of windows, so,
let the number of first floor windows be
Write the windows on the other floors in terms of
The second floor has two more:
The third floor has half as many as the second floor:
The number of windows on the the third floor =
But there are