If g(x)=2x+3g(x) = 2x + 3g(x)=2x+3 and (f∘g)(x)=8x+15(f \circ g)(x) = 8x + 15(f∘g)(x)=8x+15, find f(x)f(x)f(x).
f(x)=4x+3f(x) = 4x + 3f(x)=4x+3
f(x)=4x+9f(x) = 4x + 9f(x)=4x+9
f(x)=2x+5f(x) = 2x + 5f(x)=2x+5
f(x)=8x+3f(x) = 8x + 3f(x)=8x+3