The answer for AB is 5.
To find this answer, you would use Pythagorean Theorem. The equation would be a² + 12² = 13². First, square 12 and 13, to get the equation to say a² + 144 = 169. Next, subtract 144 from both sides. This leaves a² = 25. Finally, square root both sides to a = 5. Thus meaning 5 is the answer.
Here is an image to show how this answer is found. I hope this helps!
