Area of a Trapezoid

Put two copies of a trapezoid together, one turned upside down. They make a parallelogram whose base is the two parallel sides end to end, a + b, with the same height h. That parallelogram has area (a + b) × h, so one trapezoid is half of it.

So area of a trapezoid = ½ × (a + b) × h. Here the parallel sides are 10 and 6 and the height is 4: $\frac{1}{2}\cdot \left(10+6\right)\cdot 4 = 32$. The height is the distance between the parallel sides, at right angles to them.