statistic question

(a) A new alloy has been devised for use in a space vehicle. Tensile strength measurements X are collected from 10 pieces of alloy and the sample mean is found to be 39.3. It is reasonable to assume that the strength measurements are normally distributed with standard deviation 2.6.

i. Construct a 90% confidence interval for the population mean tensile strength.

ii. Random samples are repeatedly drawn 200 times, each with the same sample size 10. Thus we have constructed 200 90% confidence intervals for the population mean. About how many such confidence intervals would actually cover the true mean?

(b) It is stated in the contract that the average strength measurements X of the alloy should be 40. Test, at 10% significance level, is there enough evidence to say that the average strength level is actually less than 40?