To determine the distance between two points on a number line, you can use the formula:
\[ \text{Distance} = |a - b| \]
where \( a \) and \( b \) are the two numbers.
In this case, let \( a = -18.26 \) and \( b = -2.45 \). Thus, we can calculate:
\[ \text{Distance} = |-18.26 - (-2.45)| \]
This simplifies to:
\[ \text{Distance} = |-18.26 + 2.45| = |-18.26 + 2.45| = |-15.81| \]
Since the absolute value of \(-15.81\) is \(15.81\):
\[ \text{Distance} = 15.81 \]
Thus, the distance between \(-18.26\) and \(-2.45\) on a number line is:
\(\boxed{15.81}\)
Therefore, the answer is C. 15.81.