I see 4 equations and none of them indicate exponential growth, they all indicate linear change of x with respect to f(x) . . .are you forgetting to include the exponent somewhere? that would tell you which equation represents exponential growth
f(x) = 0.4(0.2)x = 0.08x
f(x) = 4(0.98)x = 3.92x
f(x) = 0.7(5)x = 3.5x
f(x) = 5(4) - x = 20 - x
