The equation \( y = x \) means that the value of \( y \) is always equal to the value of \( x \).
If the x-coordinate is 3, we can substitute that value into the equation:
\[ y = 3 \]
Thus, the ordered pair \((x, y)\) is \((3, 3)\).
Based on the options provided (1, 6, 9, 12), none of them match the ordered pair's y-value of 3. Therefore, the ordered pair satisfying the equation \( y = x \) with an x-coordinate of 3 is \((3, 3)\).