Final answer:
The transformation of the function f(x) = x into g(x) = 5x is described as a vertical stretch, because the y-values of the graph are multiplied by a factor of 5.
Step-by-step explanation:
The function g(x) = 5x represents a vertical stretch of the graph of f(x) = x. When you multiply the original function f(x) by a factor greater than 1, in this case 5, you are stretching the graph vertically by that factor. This means that for every x-value, the y-value of the graph will be 5 times higher than it was on the original graph. Therefore, the correct description of this transformation is a vertical stretch.