What’s the missing leg?!

Do you mean the length of the cable?
If so, it would be 13.42ft.
Take the cable as the hypotenuse, and add the squares of 12 and 6 then squareroot them.
Answer:
13.416ft or,
13.42ft rounded up
Step-by-step explanation:
[tex]c^2=a^2+b^2\\=6^2+12^2\\=36+144\\=180\\=\sqrt{180}\\ =13.416ft[/tex]