160 students participated in a math competition. The
participated in a math competition. The results of the competition
are as follow:
• 120 students received a score of at least 18.
Among the middle 50% of the students, 40 of them received a score lower
than 22.
The median is three-quarter the length of the interquartile range from the
upper quartile on the number scale. The two extreme values are 0 and 42.

Find the interquartile range.