Answer
$s=-2$
Work Step by Step
$Given,$ $\sqrt (s+10)=\sqrt (6-s)$
Squaring,we get:
$s+10=6-s$
$s+10+s=6-s+s$
$2s+10-10=6-10$
$2s=-4$
$s=-4\div2=-2$
We need to check by putting the obtained value in the original equation :
$L.H.S=\sqrt(-2+10) =\sqrt 8=\sqrt (6-(-2))=R.H.S$
Hence,$s=-2$ is a valid solution