To isolate \( x \) in the equation \( 5x + 8 = 63 \), Randall will subtract \( 8 \) from both sides of the equation.
Thus, he will apply the subtraction to the value \( 8 \). The equation will become:
\[ 5x + 8 - 8 = 63 - 8 \]
This simplifies to:
\[ 5x = 55 \]