Explanation:
area of a rectangle : length × width
area of a triangle : baseline × height / 2
remember, the height is at a right angle (90°) with the baseline. so, in a right-angled triangle we can use the legs as baseline and height.
length of A = 9
width of A = 5
area A = 9×5 = 45 units²
baseline of B (bottom, horizontal leg) = 13 - 9 = 4
height of B (vertical dotted leg) = 5
area B = 4×5 / 2 = 20/2 = 10 units²
the area together (the whole figure) = 45 + 10 = 55 units²