Answer:
12 m
Explanation:
Since this is a right triangle, let's use the Pythagorean Theorem.
Recall that the Pythagorean Theorem is:

Where a is the length of one of the legs, b is the length of the other leg, and c is the length of the hypotenuse.
We are given the hypotenuse (15 m) and one of the legs (9 m).
Let's assign some values:

Let's solve for b by using the Pythagorean Theorem.

So, the length of the missing leg, a, is 12 m.