The answer would be C, 12.
That already is a 91.1 grade average. If you want to keep that, get a 90 and above. To find your average, add all your test scores up and divide them by how many scores there are. For instance if you add all those scores up you get 274. Divide it by 3 because there are three scores and there is your average!
Answer is 12.73
Use Pythagorean theory
Split square into two right triangles with diagonal line. To find the diagonal
a^2 + b^2 = c^2
9^2 + 9^2 = c^2
162= c^2
Take square root of both sides
12.73 = c
(-1, 0) (0, 3)
these are the coordinates for the graph