Answer:
x=4.8
This here you use Pythagorean Theorem.
Explanation:
a^2+b^2=c^2
The longest side is c. And the two legs are a and b.
So it'd be 11^2+x^2=12^2
121+x^2=144
Subtract 121 from both sides.
x^2=23
Then take the √ of x^2 and 23
So √x^2=√23
x=4.8
Hope this helps