Since this is a half of a circle, we can find the circumference of a circle and then divide it by 2. The circumference of a circle is C = pi * D
We know that pi is 3.14 and the diameter of the circle is 3. Plug in for the variables and find the circumference.
C = 3.14*3
C = 9.42
Next, divide the circumference by 2:
9.42/2 = 4.71
The perimeter of the window is 4.71 square feet. Hope this helps.