To solve the system of equations using the substitution method, we have the following equations:
- \( x + y = 3 \)
- \( y = 8 \)
Since the second equation gives us a value for \( y \), we can substitute \( y = 8 \) into the first equation.
Substituting \( y = 8 \) into the first equation:
\[ x + 8 = 3 \]
To find \( x \), subtract 8 from both sides:
\[ x = 3 - 8 \] \[ x = -5 \]
Now we have \( x = -5 \) and \( y = 8 \). Thus, the solution for the system of equations is the ordered pair \( (-5, 8) \).
So the correct ordered pair is:
\[ \boxed{(-5, 8)} \]