Use the angle addition postulate to find the measure of each angle.

For number 15 and 16, you just have to find the absolute difference between the two points along the calibration of the protractor.

15. ∠BXC = |B - C| = |140° - 110°| = 30°
16. ∠BXE = |B - E| = |140° - 30°| = 110°

For numbers 20 and 21, apply the Angle Addition Postulate. This is when you add the individual interior angles to equate to the total angle.

20. ∠PQS = ∠PQR + ∠RQS
      112° = 72°+ 10x°
       x = 4

21. ∠KLM = ∠KLN + ∠NLM
      135° = 47°+ 16y°
       y = 5.5