The long-distance calls made by the employees of a company are normally distributed with a mean of 6.3 minutes and a standard deviation of 2.2...

1. The long-distance calls made by the employees of a company are normally distributed with a mean of 6.3 minutes and a standard deviation of 2.2 minutes. Find the probability that a call
2. Lasts between 5 and 10 minutes.
3. Lasts more than 7 minutes.
4. Lasts less than 4 minutes. 

I already get marking scheme for part a. I have no idea why suddenly 0.9535-0.2276 popped up after the step P(0.5909<Z<1.6818). Please provide the explanation as well as the answers for the remaining parts.