To rearrange the formula \( X = mb \) to solve for \( m \), you can isolate \( m \) on one side of the equation. This can be done by dividing both sides of the equation by \( b \):
\[ m = \frac{X}{b} \]
So the rearranged formula for \( m \) is:
\[ m = \frac{X}{b} \]