exponential distribution

#1
A random sample of n=20 lifetimes from an exponential distribution with mean muyielded a sample mean of 3,505 hr.
(a) Give a 90% confidence interval for the MTTF, .
(b) Give a 90% confidence interval for the reliability at t = 3,600 hr., R(3600).
(c) Compute the MLE of the 10th percentile (i.e. the 0.1 quantile), t0.1, of the lifetime distribution and a 90% confidence interval for t0.1.