Answer:
the 2nd one
Step-by-step explanation:
The answer is C. If you use the pythagorean theorem,

, and connect the two points together at a right angle and pug in the lengths of the two lines to the equation then the answer should be C.
3 because there are four sides so 3+3+3+3=12
You're right, that's the required operation.

Because they want to know how many glasses can be full, the answer is 15.