Question 14424
Try this:

{{{g(x) = 4x-1}}}
{{{g(h(x)) = 12x}}}
{{{g(h(x)) = 4(h(x))-1}}}
{{{4(h(x))-1 = 12x}}} Solve for h(x)
{{{4(h(x)) = 12x+1}}} Divide by 4.
{{{h(x) = 3x + 1/4}}}

Check: 

{{{g(h(x))= 4(3x+1/4)-1)}}}
{{{g(h(x)) = 12x + 4/4 - 1}}} = {{{12x}}}

{{{h(3) = 3(3) + 1/4}}}
{{{h(3) = 9+(1/4)}}} = {{{9.25}}}