`(x-1)(x-7)=0`
\(\Rightarrow\left[{}\begin{matrix}x-1=0\\x-7=0\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=0+1\\x=0+7\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=1\\x=7\end{matrix}\right.\)
`-------------`
`765-( 350+x)=100`
`=>350+x= 765-100`
`=>350+x=665`
`=>x=665 - 350`
`=>x= 315`