If $f: \mathrm{R}-\{0\} \rightarrow \mathrm{R}$ is defined by $3 f(x)+4 f\left(\frac{1}{x}\right)=\frac{2-x}{x}$ then $f(3)=$

• A

  $6$
• B

  $12$
• C

  $9$
• Correct answer
  D

  $3$

Hence, the correct answer is option: 'D'.