Sum of the angles

This task is about angle properties.
 Look at the diagram below and answer the questions.
sum-of-angles.png
                                                                                     [Not drawn to scale]

Question 2Change answer

a)  What is the sum, in degrees, of the angles marked 'r' and 's'?  °

Question 2Change answer

b)  i)  What is the size, in degrees, of the angle marked 'p'?  °
ii) Justify your answer.