Hello!
All of these data sets have 7 numbers, so we will not have to calculate the median by finding the mean of the two middle numbers. This means that the number 15 is inside the data set. As you can see, the last two options do not contain the number 15. So C and D are not the answer.
Let's order A and B from least to greatest.
A: 8, 9, 12, 13, 15, 16, 17
B: 6, 11, 14, 15,15,18,19
We will want to find the middle number. In this case, that is the 4th number.
Median A: 13
Median B: 15
Therefore, our answer is B) 18,15,11,14,19,15,6
I hope this helps!