`a,`
`(x - 5) . (x - 7) = 0`
`=>` \(\left[ \begin{array}{l}x - 5 = 0\\x - 7 = 0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x= 0+ 5\\x=0 + 7\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=5\\x=7\end{array} \right.\)
`b,`
`(4 + x) . (x - 3) = 0`
`=>` \(\left[ \begin{array}{l}4 + x = 0\\x - 3 = 0\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x= 0 - 4\\x= 0 + 3\end{array} \right.\)
`=>` \(\left[ \begin{array}{l}x=-4\\x=3\end{array} \right.\)
