You would want to put the function of f(x) into all of the x in g(x), so that
[tex]-3(x-7/x+3)-7/(x-7/x+3)-1[/tex]
Then you simplify and convert the constants into fractions of same value.
[tex]((-3x+21/x+3)-(7x+21/x+3))/(x-7/x+3)-(x+3/x+3)[/tex]
simplify
[tex](-10x/x+3)/(-10/x+3)[/tex]
