Answer :
[tex]y=\frac { 1 }{ 2 } x+6\\ \\ \frac { 1 }{ 2 } x=y-6\\ \\ 2\cdot \frac { 1 }{ 2 } x=2\left( y-6 \right)[/tex]
[tex]\\ \\ x=2y-12\\ \\ \therefore \quad { f }^{ -1 }\left( x \right) =2x-12[/tex]
[tex]\\ \\ x=2y-12\\ \\ \therefore \quad { f }^{ -1 }\left( x \right) =2x-12[/tex]
