Explanation
you have to replace the values in each function
Step 1
[tex]\begin{gathered} f(x)=6x+7 \\ f(x-2)=6(x-2)+7=6x-12+7=6x-5 \\ f(x-2)==6x-5 \\ \end{gathered}[/tex]Step 2
[tex]\begin{gathered} g(x)=-2x-4 \\ g(7x+1)=-2(7x+1)-4 \\ g(7x+1)=-14x-2-4 \\ g(7x+1)=-14x-6 \end{gathered}[/tex]Step 3
[tex]\begin{gathered} h(x)=\frac{-3x}{4} \\ h(-12)=\frac{-3\cdot-12}{4} \\ h(-12)=\frac{36}{4} \\ \\ h(-12)=9 \end{gathered}[/tex]I hope this helps you