In a recent issue of the IEEE Spectrum, 84 engineering conferences were announced. Four conferences lasted two days. Thirty-six lasted three days. Eighteen lasted four days. Nineteen lasted five days. Four lasted six days. One lasted seven days. One lasted eight days. One lasted nine days. Let X = the length (in days) of an engineering conference. Calculate the sample mean and sample standard deviation of days of engineering conferences. O a. x = 4.35, s = 2.17 O b. = 3.94, s = 1.28 O C. x = 2.14, s = 0.75 O d. x = 5.26, s = 3.66 QUESTION 11