You don't have a picture we can help with
You would have to begin at (2,4) to reach (5,6)
Since we are calculating the amount that he got correct, we must divide the numerator by the denominator or make the denominator equal 100. I will do it the second way as it is easier in this case.
25*4 = 100
21*4 = 84
84/100 = 0.84
As a decimal, Andrew got 0.84 of his test correct. Hope this helps!