原题：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 of the survey 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 deviation below the mean. which of the following could be the number of hours that Pat watched television last week? 正确答案是12 希望牛人给出解题步骤，先谢过了^_^ | 
