Marshall's conclusion is incorrect because he is only considering a small portion of the domains of the functions. The correct option is:
Marshall is only considering a small portion of the domains of the functions. If he went farther to the right on the graph, he would observe that the growth rate of \( f(x) = 6 \cdot 1.5^x \) eventually surpasses the growth rate of \( g(x) = 5x + 10 \) for large values of \( x \).
This is because exponential functions like \( f(x) \) will eventually grow faster than linear functions like \( g(x) \) as \( x \) increases.