What is the use or application of:

a) Waiver of Premium Rider?

b) Return of Premium Rider?

c) Please illustrate each rider using an example of someone who just purchased a disability insurance policy to age 65 with both riders included on it. Though he never got disabled throughout, he paid $ 2,000 annually from age 30 (of which the Waiver of premium cost 50/year, the Return of Premium cost $ 120/Year). How much would he receive for at the end of the policy period? Please show your calculations!