What formula do I use?

During the past year, on the average 289 books were checked out daily from the public library. This year, the library has attempted to increase circulation through various promotions. To evaluate their efforts, they have taken a random sample of 50 days of the current year and calculated the mean number of books checked out daily (301) and the standard deviation (27). Based on this data, calculate a t-score comparing the sample mean to the population mean.