What's the value of pi?

Asimple random sample of size nequals14 is drawn from a population that is normally distributed. the sample mean is found to be x overbar equals 70 and the sample standard deviation is found to be sequals13. construct a 90% confidence interval about the population mean

What is the measure of the smallest angle in the diagram? 15 29 32 45

What is the missing step in this proof ?