A trapezium has the parallel side of a length Xcm and (X-6)cm;the distance between the parallel lines is (X-3),if the area of the trapezium is 16cm,Find the height of the trapezium

since A = (b1+b2)/2*h, just solve

(x + x-6)(x-3)/2 = 16
for x. Then the height is, as they said, x-3