In the mini question why is it 135 degrees minus 120 how does 135 have anything to do with 120?

Module 2 Week 1 Day 2 Challenge Part 2 MiniQuestion
In the mini question why is it 135 degrees minus 120 how does 135 have anything to do with 120?

@TheDarkinBlade We found that \(135^{\circ}\) is the measure of one interior angle of the regular octagon, and \(120^{\circ}\) is the measure of one interior angle of the hexagon. Since the hexagon angle sits inside the octagon angle, the difference \( 135^{\circ} 120^{\circ}\) tells us the measure of the \( \textcolor{green}{\text{green}}\) sliver of an angle in this diagram: