Question 136899
Use the Pythagorean theorem.

{{{a^2 + b^2 = c^2}}}  where c is the hypotenuse of a right triangle (the long side)

You have one side (a) and the hypotenuse (c)

{{{8^2 + b^2 = 12^2}}}
{{{64 + b^2 = 144 }}}
{{{b^2 = 80}}}
b = 8.94