I immediately noticed it from an article that ran a year and a half ago in Aviation Week about a stealthy F/A-18 Hornet concept that was photographed sitting along the AMARG fence-line.

Planned to first integrate into F-22 jets and E-2D Hawkeye surveillance planes, the box collects data over time, which is continually processed by software able to calculate exactly how much the ...

The angles on a straight line always add up to 180°, so the purple angle next to it must be 100°. Image caption, STEP 4: Work out the size of the remaining angles.