Mahmut S. answered 07/16/21
Fun Math Tutor with Ed. D
since you have one interior angle of regular hexagon (120) and one interior angle of square (90) and Angle GBC forms 360 degree;
this gives us 120 + 90+ GBC=360. solve this to find GBC
we have isosceles triangle then BGC is equal to CGB, lets say BGC =x
so; x+x+GBC =180
I hope that helps