To find the point that must lie on the graph of g(5x), you need to substitute the value of 5x for x in the original point (15, 6). So, g(5x) is represented as g(5 * 15, 5 * 6):
g(5x) = g(75, 30)
Therefore, the point (75, 30) must lie on the graph of g(5x).