To find a missing side of a right triangle use the Pythagorean theorem
A2+b2=c2
C is the hypotenuse (long side)
Plug into the equation
11^2+b2=12^2
121+b2=144
So subtract 144-121 to get the missing side you get 23
Take the square root
It will be 4.7
If they want it rounded
X=5
If I had any mistakes in my answer I am sorry but everything should be correct