To solve the equation \( 12n + 34n = 12 \), we first combine the terms on the left side:
\[ 12n + 34n = 46n \]
Now, the equation becomes:
\[ 46n = 12 \]
Next, we isolate \( n \) by dividing both sides by 46:
\[ n = \frac{12}{46} \]
To simplify the fraction, we can divide the numerator and the denominator by their greatest common divisor, which is 2:
\[ n = \frac{12 \div 2}{46 \div 2} = \frac{6}{23} \]
Thus, the solution is
\[ \boxed{\frac{6}{23}} \]