Explanation:
the first wound be the sum of a
15×9 rectangle and a 15×(15-9) triangle.
the area of a rectangle is
length × width.
the area of a triangle is
baseline × height / 2.
15×9 = 135 mm²
15×(15-9)/2 = 15×6/2 = 15×3 = 45 mm²
the total area is
135 + 45 = 180 mm²
for the second I have an even easier solution :
the area is
the area of the large 14×12 rectangle minus the inner, smaller 6×9 rectangle.
so,
14×12 = 168 m²
6×9 = 54 m²
so the total area is
168 - 54 = 114 m²
the third is simply a triangle, where we got the baseline (7), although it is on the top, but that is irrelevant. and we got the height (4).
so, as in the first example, the area of a triangle is
baseline × height / 2 = 7×4/2 = 7×2 = 14 units²
the fourth :
the area of a parallelogram is
baseline × height.
do not forget, the baseline to a height (or vice versa) is identified by a right angle between each other.
so, we have
16 × 15 = 240 units²