Do you want to find the area here?

The area of an isosceles trapezoid is given by the formula

 area of isosceles trapezoid = (sum of parallel sides ÷ 2) × height

The bases height are 6 ft and 12 ft respectively which are parallel to each other,

The sum of the parallel sides = 6 ft + 12 ft = 18 ft.

height = 4ft

So plug these in the above formula to get

area of an isosceles trapezoid  =  \frac{18 ft}{2} \times 4 ft = 36 ft^{2}

I found an answer from math.stackexchange.com

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