Can I have some help with this

An oil exploration company purchases drill bits that have a life span that is approximately normally distributed with a mean equal to 71 hours and a standard deviation equal to 12 hours. (Round your answers to four decimal places.) l uses (a) What proportion of the company's drill bits will fail before 62 hours of use? (b) What proportion will last at least 62 hours? (c) What proportion will have to be replaced after more than 80 hours of use? You may need to use the appropriate appendix table to answer this question. Calculate the area under the standard normal curve between these values. (Round your answers to four decimal places.) l2 USE SALT (a) z = 1.6 andz = 1.6 (b) 2 = 2.2 and z = 1.5 You may need to use the appropriate appendix table to answer this