Marshall's mistake lies in the region of the graph he is considering. 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 • 1.5^x eventually surpasses the growth rate of g(x) = 5x + 10 for large values of x.
This is because the function \(f(x) = 6 \cdot 1.5^x\) is an exponential function and will grow faster than the linear function \(g(x) = 5x + 10\) as \(x\) increases. Although \(g(x)\) may seem greater than \(f(x)\) for small values of \(x\), eventually \(f(x)\) will exceed \(g(x)\) for sufficiently large \(x\).