Question 1017871
I'll do one you do the second one the same way.
Use x,y.
{{{y=(x-12)/4}}}
Interchange x and y and solve for y.
{{{x=(y-12)/4}}}
{{{4x=y-12}}}
{{{y=4x+12}}}
{{{f^(-1)(x)=4x+12}}}