I had a question about problem 6 on Diagnostic Drill #2 in your math book.

for IRREGULAR shapes, can you not use solely the triangle method (number of triangles x 180 degrees) to get the total interior angles? You seem to have subtracted 360 from the total number of degrees, 1080

Yeah, you have to subtract 360 for the central angles of all those triangles. That’s why the formula for the sum of interior angles, with which you might be familiar, is (n – 2)180. That simplifies to 180n – 360!