You're on the right track with isolating \( m \). To eliminate the \( 6m \) on the right side of the equation while maintaining balance, you should subtract \( 6m \) from both sides.
Here's how to do it following your equation:
Starting from: \[ 21 + 9m = 6 + 6m \]
You would subtract \( 6m \) from both sides: \[ 21 + 9m - 6m = 6 + 6m - 6m \]
This simplifies to: \[ 21 + 3m = 6 \]
Now you have all the \( m \) terms on one side of the equation. You can proceed to isolate \( m \) further by removing the constant on the left side. Would you like to move on to the next step?