standard deviation, statistics homework help

. Prof. Miller ran a marathon. Given that the mean finishing time for allrunners was 255 minutes with a standard deviation of 46 minutes and that finishingtimes were approximately normally distributed, find(a) thepercent of finishers who ran faster than Prof. Millers time of 3 hr 30 min.(b) a timethat was the 23rd percentile (23% of finishers were under that time)(c) thepercent of runners who finished between 3 hours and 4 hours(d) arandom sample of 32 runners got a special vitamin supplement right before therace. Their mean time was 4 hr 2min. What is the probability that agroup of 32 runners chosen at random would have a mean time of 4 hr 2 minutesor less?