Having trouble with this, thank you

1. Suppose that the distance of fly balls hit to the outfield (in baseball) is normally distributed with a mean of 255 feet and a standard deviation of 49 feet. We randomly sample 51 fly balls.

a)What is the probability that 51 balls traveled an average of less than 240 feet?

b)Find the 80^thpercentile of the distribution of the average of 51 fly balls.

c)What is the probability that 51 balls traveled an average of at least 309 feet?