Answer:
5
Step-by-step explanation:
Pythagorean Theorem. The 13-meter ladder is leaning against a wall, so it's the hypotenuse.
It reaches 12 meters up, so 12 is one leg.
[tex]a^{2} +b^{2}=c^{2}[/tex]
[tex]a^{2}+12^{2}=13^{2}[/tex]
[tex]a^{2}+144=169[/tex]
[tex]a^{2}=25[/tex]
a = 5
