As it is a composite shape we would split the shape up so we get a triangle and a square
Then we would work out the area of the square and the triangle
Area of a square = length x width
Area of a triangle = 1/2 base x height
Area of a square = 10 x 15 = 150
Area of a triangle = 1/2 15 x 5 = 37.5
(5 is the height of the triangle as you do 15-10 to work out the height of just the triangle
To get the total area we just combine both areas using addition
37.5+150=187.5
Answer:187.5ft squared
Hope this helped