The steps your teacher gave you are on the right track, but not quite 100% correct.
The first line has us find the area of the entire patio. That area being 110.25 square feet.
The next step is to find the area of each stone. That would be 1.5 x 1.5 = 2.25 square feet.
Therefore, the patio is made up of 110.25 ÷ 2.25 = 49 tiles
When arranged into a square, we'll have a 7 by 7 square set of stone tiles. Notice how 7 x 7 = 49.
