Sermons My Daughter and I Have Argued About the Average Length

Short Answer

Sermons
My daughter and I have argued about the average length of our preacher's sermons on Sunday morning.Despite my arguments,she thinks that the sermons are more than twenty minutes (over twenty minutes is important to her especially when soccer was playing on TV).For one year she has randomly selected 12 Sundays and found the average time of 26.42 minutes with a standard deviation of 6.69 minutes.Assuming that the population is normally distributed and using a 0.05 level of significance,is my daughter correct in thinking that the average length of sermons is more than 20 minutes?
What is the value of test statistic t?