Answer:
10.9
Step-by-step explanation:
You can solve this using the Pythagorean theorem, a^2+b^2=c^2, since it will form a right triangle.
You aren't missing the hypotenuse (c), but one of the side lengths (b). But you still solve like a normal algebraic equation.
Plugging in your values, you should start with 5^2+b^2=12^2
Then square everything.
25+b^2=144
Take away 25 from both sides.
b^2= 119
Then square root both sides.
b= 10.9