You don't provide much info here. Â A drawing of the wall would be useful. Â You'll need to choose variables (x, y, h, and so on) to represent the dimensions of the trapezoid and its parts (the rectangular bottom part and the triangular top part). Â The area of the trapezoidal shape is the sum of the areas of the rectangle and the triangle.
Suppose that the horiz. measurement of the rectangle is x and that the vertical meas. is y. Â Then the area of the rectangle is Ar = xy.
Suppose that the horiz. base of the triangle is x (same as the horiz. measurement of the rectangle. Â Let the vert. height of the triangle be y.
Then the area of the triangle is At = (xy)/2 (standard formula for the area of a triangle)
Then the area of the trapezoid is the sum of the areas of the rectangle and triangle:
A = xy + (xh)/2
Without more info (e. g., the values of x, y and h), we can proceed no further.