Answer:
1 (square root of 72)
Explanation:
Ok. You can solve this using the pythagorean thereom. This is because AB is the hypotenuse of a right triangle. Therefore, you can solve this problem by using the square of both sides to find the length of the hypotenuse. 6^2+6^2=c^2.
36+36=72
=8.5
8.5 is about what the line looks to be just by eyeing it, and it fits in with the theroem used, therefore I'd say it is #1. Hope that helps.