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.

the data is shown in the table below.

number of conferences

days lasted

4

2

36

3

18

4

19

5

4

6

1

7

1

8

1

9

calculate the sample mean of days of engineering conferences.