We want to fill in the blank in the equation;
let's represent the blank with a.
[tex]_{}a(x+6)+8(x+6)=4x+24[/tex]Let's factorize the right side of the equation.
[tex]\begin{gathered} a(x+6)+8(x+6)=4x+24 \\ a(x+6)+8(x+6)=4(x+6) \end{gathered}[/tex]and also the left side;
[tex]\begin{gathered} a(x+6)+8(x+6)=4(x+6) \\ (a+8)(x+6)=4(x+6) \end{gathered}[/tex]Then let's divide both sides by (x+6);
[tex]\begin{gathered} (a+8)(x+6)=4(x+6) \\ \frac{(a+8)(x+6)}{(x+6)}=\frac{4(x+6)}{(x+6)} \\ (a+8)=4 \end{gathered}[/tex]Then we can solve for a in the resulting equation.
subtract 8 from both sides.
[tex]\begin{gathered} a+8=4 \\ a+8-8=4-8 \\ a=-4 \end{gathered}[/tex]Therefore, the value to fill into the blank is -4
[tex]-4(x+6)+8(x+6)=4x+24[/tex]