Cross section area = 1/2 x ( a + b ) x d where a and b are the parallel sides, d is the perpendicular distance between them.? 1/2 x ( a + b ) x d = 640? d = (640 x 2) / 16 = 80m
Area of a triangle formed by joining the mid point of the sides of the triangle is 1/4th of area of the original triangle .So area of ? DEF = 36/ 4 = 9 m2