Question

The stem-and-leaf plot represents the average monthly high temperatures in Tampa, Florida. What is the third quartile (Q3) of the temperatures?

Answer 1

Your stem plot is short hand for the numbers
69 71 72, 76 77 81, 84 87 89, 89 90 90
the 3rd quartile is the set 84 87 89

Answer 2

The answer that I get to choose from are
A. 85
B. 87
C. 88
D. 89

Answer 3

In that case, the third quartile is the median of the numbers above the median.
In your data, with 12 numbers, the 6 largest numbers are above the median
84 87 89 89 90 90
the median of an odd number of entries is the middle number. The median of an even number (which is our case here), it is the average of the 2 middle numbers.
The 2 middle numbers are 89 and 89. Their average is 89. Choice D