70, 75, 80, 85, 90, 105, 105, 130, 130, 130

the list shown consists of times, in seconds, that it took 10 schoolchildren to run a distance of 400 meters. if the standard deviation of the 10 running times is 22.4 seconds, rounded to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times?

answer choices:
1
2
3
4
5


please shed some light on this problem