Supplementary angles are two angles whose measures add up to 180 degrees.
Given that \( m∠j = 34° \), you can find \( m∠k \) using the following equation:
\[ m∠j + m∠k = 180° \]
Substituting the known value:
\[ 34° + m∠k = 180° \]
Now, solve for \( m∠k \):
\[ m∠k = 180° - 34° \]
\[ m∠k = 146° \]
Therefore, \( m∠k = 146° \).