Explanation:
it clearly consists of 2 rectangles and 1 triangle (as you tried correctly to point out by drawing the separating lines).
we only need to calculate all 3 areas and add them up for the total.
the area of a rectangle is
length × width
so, in our 2 cases we have
6 × 2 = 12 km²
5 × (3 + 2 + 3) = 5×8 = 40 km²
the area of a triangle is
baseline × height / 2
in case of a right-angled triangle the 2 sides enclosing the 90° angle can be used as baseline and height.
so, in our case
6 × (5 + 2 + (3 + 2 + 3 - 2)) / 2 = 6×(7 + 6)/2 = 3×13 = 39 km²
in total, the whole area is
12 + 40 + 39 = 91 km²