To find the area of the composite figure, we need to calculate the area of each individual rectangle first and then add them up.
Area of the original rectangle:
Length = 7 miles, Width = 3 miles
Area = Length x Width = 7 miles x 3 miles = 21 square miles
Area of the left side rectangle extension:
Length = 6 miles, Width = 3 miles
Area = Length x Width = 6 miles x 3 miles = 18 square miles
Area of the right side rectangle extension:
Length = 1 mile, Width = 1 mile
Area = Length x Width = 1 mile x 1 mile = 1 square mile
Total area = 21 square miles + 18 square miles + 1 square mile = 40 square miles
Therefore, the area of the composite figure is 40 square miles.