The interquartile range (IQR) is 15.
To find the IQR, you must:
1) Find the median
2) Split the data set in two at the median.
3) Find the medians from both the groups you made in Step 2
4) Label the smaller one Quartile 1 and the larger one Quartile 3 (Hint: The median is Quartile 2)
5) Subtract: Quartile 3 - Quartile 1