to solve this you would use the Pythagran Theorem, a^2+b^2=c^2. I counted the square units on the graph to find the length of the legs, 4 and 5. Then, I plugged them into the equation to get 16+25=c^2, which is 40=c^2=
[tex] \sqrt{40} [/tex]
and if you type sqrt40 into a calculator you get about 6.4. So the answer would be D.
