Explanation:
Let's see
Firstly produce the line to Q such that it passes through and dives Q into two.
The interior angle of the Pentagon at the point Q=sum of its interior angle/5
The angle=540°/5=108°
That would make the exterior angle there=180°-108°=72°
Again,find the interior angle of the heptagon at the point Q=(sum of its interior angles)/7
Angle=900°/7=128.57°≈129°
That would make the exterior angle there=180°-129°=51°
Since Q was divided into the two exterior angles,we sum them up to obtain the angle value of Q
That is 51°+72°=123°