Question 1040459
x in the defined function is a dummy variable.  You could call it r if you wish to, and say,  {{{g(r)=3r^2-4r}}}.


Next, you want to find what is  g(5x), in which r=5x.
{{{g(5x)=3(5x)^2-4(5x)}}}
{{{highlight(75x^2-20x)}}}