If the graph of g is a vertical stretch by a factor of 4 of the graph of f, then for any value of x, the value of g(x) is 4 times the value of f(x). This means that we can write the function g in terms of f as follows:
g(x) = 4f(x)
This means that for any value of x, the value of g(x) is equal to four times the value of f(x).