Could you explain the steps/formulas used to solve this practice problem?

A new startup gifting company says that they can deliver 95% of all local orders within 2 hours. They decide to demonstrate this by using their first 100 orders to demonstrate their delivery promise.

a. Assuming the delivery time for each order is independent, what is the probability that 85% or fewer orders will be delivered within 2 hours?

b. The company's first 100 orders resulted in 82 deliveries within 2 hours. What is the 95% confidence interval for the population proportion of deliveries made within 2 hours of the order being placed?