To isolate \( x \) in the equation \( 5x + 8 = 63 \), Randell will first use subtraction to remove the constant term from the left side. He needs to subtract the \( 8 \) on the left side.
So, the value he will apply in the subtraction operation is \( 8 \).
This operation will look like this:
\[ 5x + 8 - 8 = 63 - 8 \]
Which simplifies to:
\[ 5x = 55 \]
Randell can then continue to solve for \( x \).