You read a steam and leaf plot in this way: the first column is the first digit of the score, and we're grouping scores by their first digits.
So, for example, if we read the row starting with 5, we deduce that there have been three scores in the 50's, namely two 57 and one 58.
To answer the question, we have to count how many occurrences we have in the row of the 70's and higher.
We have 4 scores in the 70's: 70, 70, 71, 78
We have 4 scores in the 80's: 82, 84, 87, 88
We have 3 scores in the 90's: 91, 93, 97
We have 2 perfect scores of 100.
These are all the scores of 70 or above.