Me with this question (bottom question)

This is another one for the "impossible geometry question" file.

Answering the last question first, the sum of exterior angles of any convex polygon is 360°.

This fact tells us that the sum of interior angles is 10*180° - 360° = 1440°. Without additional information, we do not know the measure of each interior or exterior angle.

If we assume all angles are equal, then
  Each interior = 1440°/10 = 144°
  Each exterior = 180° -144° = 36°

The answer is b: step 2.