There are 10 values in the data set. Conveniently, they are sorted for you. The median (central line in the box) will be the average of the middle two numbers:
.. (20 +22)/2 = 21 . . . . . . . . matches the 2nd and 4th selections
The first quartile (the left end of the box) will be the middle number of the first group of 5, so is 9. This matches the 4th selection only.
The 4th selection is appropriate.
