To isolate \( x \) in the equation \( 6x + 3 = 5(x + 3) \), which simplifies to \( 6x + 3 = 5x + 15 \), we can get rid of the \( 5x \) term on the right side by subtracting \( 5x \) from each side of the equation.
So, the correct move would be:
Subtract \( 5x \) from each side.
This results in:
\[ 6x - 5x + 3 = 15 \]
or simply:
\[ x + 3 = 15 \]
Now you can continue to solve for \( x \).