Reading bar charts: comparing two sets of data

So we have this bar chart here. This says Scores on Midterm and Final Exams. So this axis, the vertical axis, is the scores. And then it's by student. And the blue bar is the midterm, and the yellow bar is the final. And the question they ask us is by how many points did Nadia's score improve from the mid-term to the final exam? So let's look at Nadia. So this is who we're talking about-- Nadia. And we care about how many points did she improve from the midterm to the final. Midterm is blue, final is yellow. So on the midterm, it looks like she scored-- and if I were to eyeball it, it looks like 75 points. And on the final, it looks like she scored 80. It looks like she scored 85 points. So it looks like her score improved by 10 points, so 10 points. Let's try one more. How many students improved their scores from the midterm to the final exam? So to improve from the midterm to the final, that means that the yellow bar for a given student, which is the final, is going to be higher than the midterm bar. That's the only way you can improve from the midterm to the final. So Brandon improved from the midterm to the final. Vanessa improved from the midterm to the final. Daniel improved from the midterm to the final. Kevin improved from the midterm to the final. William got a lower score on the final than the midterm, so he did not improve. So the number of students that improved their scores from midterm to final are one, two, three four students, so 4 students.