Answer:
89 meters
Step-by-step explanation:
We know it's 9 + "the height of the triangle".
Fortunately, the height of the triangle (let's call it y) can be computed from:
y^2 + 18^2 = 82^2 (Pythagoras theorem).
y^2 = 82^2 - 18^2 = 6724 - 324 = 6400
y = 80 (or y = -80 but it doesn't make sense in geometry).
so x = y + 9 = 89;
