Answer:
b
Explanation:
Let's find the area of the adjacent side.
Applying Pythagoras' Theorem,
(adjacent side)²= 18² -9²
adjacent side

adjacent side= 15.588 m (5 s.f.)
Area of triangle= ½ ×base ×height
Area of traingle

The nearest answer is B.
*If you rounded of to the nearest tenth for the adjacent side first then use the formula for area of traingle, the result would be exactly 70.2 m.