how do you do area of trapezoids
you have to do height ÷ 2 ×(base one+ base two) = area of a trapizod
I think what you are calling a trapezoid I would call a trapezium.
Your formula is corect but this is how I think of it.
Area = average of the parallel sides x perpendicular height.
$$area = \frac{(a+b)}{2}\times h$$