The answer is b, tell me if you don't understand.
Hello!
We use different formulas to calculate the areas of different shape.
RECTANGLE:
To find the area of a rectangle, we must simply multiply its length by its width. The formula for its area is:
A = l × w
SEMICIRCLE:
Since the formula for a circle is pi × r × r, we must use the same formula but divide it in half, because a semicircle is a half circle, which is why its area would also be half of a circle's. The formula for a semicircle's area is:
A = 1/2 pi × r × r
Tip:
Write these formulas down and memorize them so that you don't forget them. You'll have to use these formulas quite often when finding the area of these shapes.
The Reuleaux triangle is shown in the attached figure
we know that
the area of a Reuleaux triangle is equal to

where
r=18.6/2--------> r=9.3 m
so


therefore
the answer is
61 m²