Percentage of Students Reading Between 9 and 15 Books

A researcher is analyzing data from a recent survey conducted among students in a high school. The survey recorded the number of books read by each student during the summer. After compiling the data, the researcher finds that the mean (average) number of books read is 12, with a standard deviation of 3 books. Assuming the number of books read follows a normal distribution, what is the approximate percentage of students who read between 9 and 15 books?

Use the empirical rule (68-95-99.7 rule) for normal distributions to help in your calculations.