Respuesta :

A = 1/2 h (b1+b2)
so
h = 2A / (b1+b2)
h = [2(3x^2 + 5x)] / (2x + 1 + x + 4)
h = (6x^2 + 10x)/(3x +5)
h = 2x(3x + 5)/(3x +5)
h = 2x

answer: 
height of a trapezoid = 2x