The main lesson students and teachers should take away from this problem is the correct answer should be: who cares? The group built their frames with a ruler and a saw, got an exact slope of 10/3 and the angle measures didn't matter one bit. The best angles measures are the ones avoided.
But trig as taught is all about angles. Gotta find the angle. Here we have a right triangle and we're interested in the angle at the top of the frame, opposite side 3, adjacent side 10, so
[tex]\tan \theta = \dfrac{3}{10}[/tex]
[tex]\theta = \arctan \dfrac{3}{10} \approx 16.7^\circ[/tex]
