Suppose that the lifetimes of a certain kind of light bulb are normally distributed with a standard deviation of 120 hours. If exactly 98% of the bulbs die before 920 hours, find the mean lifetime of...

Suppose that the lifetimes of a certain kind of light bulb are normally distributed with a standard deviation of 120 hours. If exactly 98% of the bulbs die before 920 hours, find the mean lifetime of the bulbs. Carry your intermediate computations to at least 4 decimal places. Round answer to at least 1 decimal place.