To find the value of \( m∠7 \), we can use the fact that angles on a straight line sum to \( 180^\circ \).
In this case, angles \( m∠7 \) and \( m∠8 \) are adjacent angles that form a linear pair (they are supplementary). Therefore, we can set up the equation:
\[ m∠7 + m∠8 = 180^\circ \]
Given that \( m∠8 = 45^\circ \), we can substitute that into the equation:
\[ m∠7 + 45^\circ = 180^\circ \]
Thus, the equation that can be written to find the value of \( m∠7 \) is:
\[ m∠7 + 45^\circ = 180^\circ \]