Answer: The correct option is second, i.e.,
.
Explanation:
A functions g(x) is stretch or compressed of graph of function f(x) is defined by the equation,

Where, k is a constant and it shows the compress or stretch factor.
If k>0, then it is a stretch factor and the graph of f(x) is stretched by factor of k.
If k<0, then it is a compress factor and graph of f(x) is compressed by factor k.
Since the graph of g(x) is a vertical stretch of the graph of function f(x) by a factor of 3, therefore,

So, the option second is correct.