Type the correct answer in the box. Use numerals instead of words. If necessary, use / for the fraction bar.
This data set represents the number of cups of coffee sold in a café between 8 a.m. and 10 a.m. every day for 14 days.

{10, 9, 6, 12, 4, 6, 7, 8, 15, 14, 12, 9, 10, 5}.

The difference of the values of the first and third quartiles of the data set is