#### Answer

$12$

#### Work Step by Step

$\log _{2}\left( x^{2}-100\right) -\log _{2}\left( x+10\right) =1\Rightarrow \log _{2}\left( \dfrac {x^{2}-10^{2}}{x+10}\right) =1$
$\dfrac {\left( x-10\right) \left( x+10\right) }{\left( x+10\right) }=2^{1}\Rightarrow x-10=2\Rightarrow x=12$