To solve the system of equations using substitution, we have the following equations:
- \( y = 9 \)
- \( 7x - 4y = 6 \)
Since we already have \( y \) expressed in terms of a constant (9), we can substitute \( y \) into the second equation.
Substituting \( y = 9 \) into the second equation:
\[ 7x - 4(9) = 6 \]
Now simplify this equation:
\[ 7x - 36 = 6 \]
Next, add 36 to both sides to isolate the term with \( x \):
\[ 7x = 6 + 36 \] \[ 7x = 42 \]
Now, divide both sides by 7 to solve for \( x \):
\[ x = \frac{42}{7} = 6 \]
Now we have the values:
\[ x = 6 \quad \text{and} \quad y = 9 \]
Thus, the solution to the system of equations is:
\[ (6, 9) \]
So the final answer is:
\[ \boxed{(6, 9)} \]