To the left of the vertical bar are the tens places. As we want to find the scores greater than 90, we start at the row in the stem and leaf plot with a 9 to the left. To the right are 6 values - 1, 2, 3, 4, 6, and 7. So there are six scores here higher than 90: 91, 92, 93, 94, 96, and 97. Now we move lower to 10 in the tens place. There is one score there - 100. (That smart kid.)
Total up the six scores in the 9 row and the 1 in the 10 row to get 7 scores higher than 90 in this stem and leaf plot.
Thus, there are 7 scores - choice B - in the plot higher than 90.