Since ∠3 and ∠5 are vertical angles, we have:
\[ m∠3 = m∠5 \]
Given that \( m∠3 = 67° \), it follows that:
\[ m∠5 = 67° \]
Now, since ∠4 is supplementary to ∠5, we know that:
\[ m∠4 + m∠5 = 180° \]
Substituting for \( m∠5 \):
\[ m∠4 + 67° = 180° \]
So, the equation you can write to solve for \( m∠4 \) is:
\[ m∠4 + 67° = 180° \]