Suppose the number of cars passing a point on a highway follows a Poisson distribution with a mean of 4 cars per minute. (a) What is the probability that no cars pass the point in one minute? (b) What is the probability that two cars pass the point in 30 seconds? (c) What is the probability that 6 cars pass the point in 2 minutes? (d) What is the probability that at least one car passes the point in 15 seconds?