The monthly utility bills in a city are normally​ distributed, with a mean of $100 and a standard deviation of $15. Find the probability that a randomly selected utility bill is​ (a) less...

The monthly utility bills in a city are normally​ distributed, with a mean of $100 and a standard deviation of $15.

Find the probability that a randomly selected utility bill is​ (a) less than ​$69​,​(b) between ​$86 and $100​, and​ (c) more than ​$120.