Andrea’s backyard is 400 square feet. Her rectangular swimming pool is 10 feet long, and six feet wide. What is the area of Andrea’s backyard, not including the swimming pool?

First, you have to find the area of the rectangular swimming pool (A1), which has 10 feet long and 6 feet wide. The area of a rectangle is:

 A=A1=LxW

 L=10 ft
 W=6 ft

 When you substitute these values into the formula, you obtain:

 A1=LxW
 A1=(10 ft)(6ft)
 A1=60 ft²

 The area of the Andrea’s backyard (A2) is 400 ft², therefore, the area of Andrea’s backyard, not including the swimming pool (A3), is:

 A3=A2-A1
 A3=400 ft²-60 ft²
 A3=340 ft²

 What is the area of Andrea’s backyard, not including the swimming pool?

 The answer is: The area of Andrea’s backyard, not including the swimming pool, is 340 feet²