The height of the trapezoid is 3 because the triangle is a 3-4-5 triangle (Pythagorean triplets).
Now find area of the rectangle by L*W.
The area of the rectangle is 12.
Now find the area of the triangle.
Area of a triangle is height * base /2.
Therefore the area of the triangle is 4*3/2=6.
Now combine the area of the rectangle and triangle.
The area of the trapezoid is 18.