You can find the medians by referring to the line in the middle of both of the boxes. These indicate the median of the sets of data you have. The first median is at 10 and the other is at 12.
All you need to do to find the difference is subtract the smaller number from the bigger number.
12 – 10 = 2
Your difference will be 2, making your second option your answer. Hope this helped you out! :-)
