What is the value of the second quartile (q2) of the data set?

45, 51, 52, 58, 61, 63, 66, 72, 74

You're trying to find the second quartile (Q₂), and to find that, you must find the median, and then find the median within the second half of the median :)

Median (Middle Number) : 61

Now, look at 61, and look at 74. What is the median of those numbers in this set?

Q₂ = 66

So, your quartile 2 is 66.

~Hope I helped!~