A factory produces car tires. The number of miles each tire lasts before it completely wares out follows a normal distribution with mean u = 50,000 miles and standard deviation a = 8,000 miles. If the tires last for less than 30,000 miles, customers will complain. What is the probability for a randomly selected tire to last less than 30,000 miles, i.e., P(x $ 30,000)