68% of all Americans live in cities with population greater than 100,000 people. If 30 Americans are randomly selected, find the probability that a. Exactly 18 of them live in cities with population greater than 100,000 people. b. At most 19 of them live in cities with population greater than 100,000 people. c. At least 18 of them live in cities with population greater than 100,000 people. d. Between 15 and 23 (including 15 and 23) of them live in cities with population greater than 100,000 people.

Please show all the work so I can understand how to solve this equation.