Please explain including the formulas. Thank you!

4.10.3) The length of time (in seconds) that a user views on a Web site before moving to another page is a lognormal random variable with parameters 3 = 0.7 and m2 = 1. (a) What is the probability that a page is viewed less than 15 seconds? (b) By what length of time have 70% of the users moved to another page? (c) What are the mean and variance of the time until a user moves from the page