Given that \( m\angle 8 = 45^\circ \), we can analyze the relationship between the angles in the trapezoid and triangles.
Since angles \( \angle 7 \) and \( \angle 8 \) are adjacent angles on a straight line (the top line of the trapezoid), they are supplementary. Therefore, we can write the equation:
\[ m\angle 7 + m\angle 8 = 180^\circ \]
Substituting the given value for \( m\angle 8 \):
\[ m\angle 7 + 45^\circ = 180^\circ \]
Thus, to find the equation you are looking for:
\[ m\angle 7 + 45^\circ = 180^\circ \]