The area of any trapezoid is
                    (1/2) (height) (sum of the bases) .
For the trapezoid in the picture:
The height         = 15 mm
One base          =   14 mm
The other base =  36 mm
-- Add the two bases.
-- Multiply the sum by the height.
-- Take 1/2 of the product.
The result is the area.