The following data shows the average time span of international phone calls by a

sample of 15 executives of a company having operations overseas:

time in (minutes)

12.0 15.0 16.3 13.2 12.6 18.2 8.7 13.5

16.9 11.3 15.4 16.2 12.6 10.5 9.6 6.0

an approximate 95% confidence interval for the average time span of calls is

(a) 11.244 to 14.756

(b) 12.344 to 15.856

(c) 10.564 to 14.876

(d) 12.831 to 16.667

(e) 13.453 to 15.887