For this case what you should do is find the area of the rectangle and the are of the triangle.
Area of the rectangle:
A1 = (6) * (7)
A1 = 42 in ^ 2
Triangle area:
A2 = (1/2) * (6-3) * (13-7)
A2 = 9 in ^ 2
The total area is the sum of both areas:
A = A1 + A2
A = 42 + 9
A = 51 in ^ 2
Answer
the area of this composite shape is
A = 51 in ^ 2