To solve the equation \( 7y = 12x \) for \( y \), we will isolate \( y \):
- Divide both sides of the equation by 7:
\[ y = \frac{12x}{7} \]
This can also be written as:
\[ y = \frac{12}{7} x \]
Therefore, the correct answer is:
C. \( y = \frac{12}{7} x \).