The amount of time it takes a student from school A to do a math activity follows the Normal distribution with a mean of 25 minutes and a standard deviation of 5 minutes. Students at school B complete a math activity with a mean time of 20 minutes and have a standard deviation of 8 minutes.

a.) If we take a random student from School A and a random student from School B. What is the expected difference in their minutes?

b.) What is the standard deviation of the difference of their minutes?