To solve the equation \( \frac{m}{6} + 5 = 18 \), the first operation you would need to perform on both sides is to subtract 5 from each side. This will help to isolate the term with \( m \) on one side of the equation.
So, the operation is:
\[ \frac{m}{6} + 5 - 5 = 18 - 5 \]
This simplifies to:
\[ \frac{m}{6} = 13 \]
After this first step, you would continue solving for \( m \).