Sheryl has a Christmas lighting project. She is going to put lights around outside of 15 windows with a height of 4 feet and a width of 2 feet. She also wants to put lights around 3 garage doors that are 9 ft wide and 9 ft long. How many feet of Christmas lights will be needed

She will need 288 ft of Christmas lights

Step by Step:
First we find how many feet is needed to go around 1 window. We do this by adding up all four of its sides.
4+4+2+2= 12
Because there are 15 windows be multiply the feet needed for 1 window by 15.
12•15=180
Repeat the first two steps for the garage doors to find that she needs 108ft of lights for 3 garage doors and add the feet needed for the windows to the feet needed for the garages
180+108=288

Where are the calculations?