The polynomial is given as,
[tex]y^2\text{ - 16 and 5y + 20}[/tex]Simplifying the first expression,
[tex]\begin{gathered} y^2-16=y^2-4^2 \\ y^2-16=\text{ ( y - 4 )( y + 4 )} \end{gathered}[/tex]Simplifying the second expression,
[tex]5y\text{ + 20 = 5( y + 4)}[/tex]The common factor is given as,
[tex]\text{Common factor = ( y + 4 ) }[/tex]Uncommon factors are given as,
[tex]\text{Uncommon factor = ( y - 4 ) }\times\text{ 5}[/tex]LCM is calculated as,
[tex]\text{LCM = 5}\times(\text{ y - 4 )( y + 4 )}[/tex]Thus the LCM of the given expression is,
[tex]\text{ 5}\times(\text{ y - 4 )( y + 4 )}[/tex]