For Interquartile Range (IQR) you use the box and whiskers. The line at the far left hand side (the left whisker) is the lowest value of your data and the line at the far right hand side (the right whisker) is the highest value of the data set. These values are not used for the IQR. The left hand side of the box is your lower quartile, this is the median of the lower half of the data set. The right hand side of the box is your upper quartile, this is the median of the upper half of the data set. The line in the middle of the box is the median for the entire data set. IQR refers to the range (which is the difference or answer to a subtraction problem) of the upper quartile and lower quartile. Make sure to always pay attention to the scale of the number line, the largest box does not always mean the largest IQR. In this case though, choice B has an upper quartile of 85 and a lower quartile of 60. When you subtract 85 - 60 the difference is 25 which is your IQR and the other box and whisker plots have an IQR of 10.
