An interquartile range is finding the median of the first half of the data set, and the second half, then subtracting the first median from the second one.
Note the location of the vertex (point A) on the graph. Its x-coordinate is readily identifiable as 1. Its y-coordinate is some value between -15 and -20, closer to -15. (If you go to the trouble of finding the vertex coordinates, you discover they are (1, -16).)
Once you have determined what the vertex is, you can compare the offered answer choices to the vertex form ...
y = (x -h)² +k
where (h, k) are the vertex coordinates. That is, you are looking for an answer choice that is something like ...
