To solve this problem, let's break it down step by step.
Let's assume that the ladder has x rungs.
According to the given information, the firefighter stood on the middle rung of the ladder, which means that the middle rung is located at position (x + 1) / 2.
Next, the firefighter climbed up 6 rungs, so the new position of the firefighter is now at (x + 1) / 2 + 6.
After that, the firefighter came down 10 rungs, so the new position is (x + 1) / 2 + 6 - 10.
Finally, the firefighter climbed 18 rungs to reach the very top of the ladder, which means the new position is (x + 1) / 2 + 6 - 10 + 18.
According to the given information, the final position is equal to x, which means:
(x + 1) / 2 + 6 - 10 + 18 = x
Simplifying this equation, we get:
(x + 1) / 2 + 14 = x
Multiplying both sides of the equation by 2 to eliminate the fraction, we get:
x + 1 + 28 = 2x
Combining like terms, we get:
x + 29 = 2x
Subtracting x from both sides of the equation, we get:
29 = x
Therefore, the ladder has 29 rungs.
Hence, the correct answer is C) 29.