The graph y=g(x) is the graph of y=f(x) escalated horizontally by expansion by a factor of 3 and escalated vertically by expansion by a factor of 4.
Since the graph of y=f(x) is stretched horizontally by factor 3, therefore, the new graph will be
[tex]y=f(\frac{1}{3}x)[/tex]
Again, it is stretched vertically by a factor 4 and 4>1.
Therefore, the equation of y=g(x) in terms of f(x) is
[tex]g(x)=4f(\frac{1}{3}x)[/tex]
