Hi

the 68-95-99.7 rule:
one  standard deviation from the mean accounts for about 68.2% of the set 
two standard deviations from the mean account for about 95.4%
and three standard deviations from the mean account for about 99.7%.

?, and ?% of the data is either less than 4.2 or more than 11.4.
  (11.4-4.2)/4 = 1.8 SD
 Between 4.2 and 11.4 account for 95%  (Each are 2 SD from mean of 7.8)
0r
 5% of the data is either less than 4.2 or more than 11.4. 

The standard deviation of this data is 1.8, and 5% of the data 
is either less than 4.2 or more than 11.4.

Wish You the Best in your Studies.