The only information you need to know to solve for angle 7 is
1. Supplementary angles add up to 180 degrees.
2. Angle 8 is 124 degrees.
7 and 8 are supplementary angles, which means they add up to 180 (respectively, a full turn equals 360 degrees). You can use a simple subtraction problem to solve for angle 7.
180-124=m∡7
m∡7= 56.
Angle 7 is 56 degrees.
Hope this helps!