ANSWER :
The equation of g(x) is :

EXPLANATION :
Note that stretching a function horizontally by a factor of c :

From the problem, we have a function f(x) = x^2
and g(x) is the graph of f(x) when horizontally stretched by a factor of 3.
Then :

Substitute x/3 to the parent function f(x) = x^2 :
