I have a math problem i need help with. Thank you.

Problem:
let's say there is a 15% chance of getting strep if you are exposed to a person with strep. Let’s say there is a 50% chance that you were exposed.
a) What is the probability that
you will get strep?

b) Let’s say each person in your (4-person) family had a 50% chance of being exposed. What is the probability that you will get strep?