Step 1: Mode formula in terms of mean and median.
The mode of a distribution can be calculated using the empirical relationship:
\[
\text{Mode} = 3 \times \text{Median} - 2 \times \text{Mean}
\]
Step 2: Applying the values.
Given that the mean = 17 and the median = 18, we substitute these values into the formula:
\[
\text{Mode} = 3 \times 18 - 2 \times 17 = 54 - 34 = 18.5
\]
Step 3: Conclusion.
Therefore, the mode of the distribution is \( \boxed{18.5} \). The correct answer is (3) 18.5.