a)What is the probability that a randomly selected baggage item weighs more than 15kg?

This is what I have come up with;

To Get Z = (data point - mean) / standard deviation

Z = (15-13) / 3.1

Z = 0.645

P( X > 0.645) = 0.740

Im not sure where to start with this one;

b)What is the probability that a sample of 10 baggage items weighs more than 150kg in total?

c)What is the 80th percentile of checked-in baggage weight (such that 80% of baggage items weigh less than this amount).

This is my work so far for this question, I got the answer out from doing the calcs in the computer system they have asked us to use but Im not sure how to work it out myslef with a formula.

P ( X < a) = 0.80

P (X < 0.80) = 15.61

Again, I dont know where to begin with this

A random sample of 30 baggage items resulted in a mean weight of 13.544 kg and standard deviation 2.709 kg. Find 95% confidence intervals for

i. the population mean weight.

ii. the population standard deviation of weight.

Any assistance would be very much appreciated. Thank you