Please explain the steps and how to do this:

As an analyst for a mobile device manufacturer, you have noticed that customers between 18 and 24 years of age spend an average of 325 minutes per month watching video on their device. The standard deviation of the time they spend is 50 minutes. Assuming the time spent watching video by this consumer demographic is approximately normally distributed, find the following probabilities:

(A) A randomly selected 18-24 year-old customer watches video for less than 300 minutes.

(B) Find the probability that a randomly selected 18-24 year old customer watches video for more than 400 minutes.

(C) Find the probability that a randomly selected 18-24 year old customer watches video for less than 400 minutes.

(D) Find the probability that a randomly selected 18-24 year old customer watches video for between 300 and 400 minutes.