Hi there!
We can look at each function, f(x) and g(x), to determine which is exponential.
Use slope formula: m = y2-y1/x2-x1
f(x) starts off with a slope at about $1800/year, but becomes about $1100/year.
g(x) starts off with a slope of about $1500/year, but becomes about $1874/year.
Thus, g(x) is exponential, because g(x)'s slope is increasing across the interval.