To find \( m∠7 \), we can use the property that angles on a straight line sum up to \( 180° \).
Since \( ∠6 \) and \( ∠7 \) are adjacent angles, we know:
\[ m∠6 + m∠7 = 180° \]
Given that \( m∠6 = 140° \), we can substitute this value into the equation:
\[ 140° + m∠7 = 180° \]
Now, we can solve for \( m∠7 \):
\[ m∠7 = 180° - 140° = 40° \]
Thus, the measure of angle \( ∠7 \) is:
\[ \boxed{40°} \]