We want to find the percentage of students that scored between 70-90 points on the examn. Also, we know that there are a total of 71 students, so we have to count the number of students who got between 70-90 points.
We see them represented on the histogram as the two largest bars, and we obtain:

So, the total of students that scored between 70-90 points is 21+22=43.
For finding the percentage, we make the quotient between the number of students with a score of 70-90 and the total of the students in the class.

This means that approximately a 60.6% of the class students scored between 70 and 90 points.