Hey guys here is the question

The residents of Town X participated in a survey to determine the number of hours per week each resident spent watching television. The distribution of the results had a mean of 21 hours and a standard deviation of 6 hours. The number of hours that Pat, a resident of Town X, watched television last week was between 1 and 2 standard deviations below the mean. Which of the following could be the number of hours that Pat watched television per week.
30;20;18;12;6

Following my calculations the answer should be 18, but at the end it's 12. What am I doing wrong?