lim(x→0) (1 + 3x)^(3/x)
= lim(x→0) (1 + 3x)^[1/(3x) * (3x) * 3/x]
= [lim(x→0) (1 + 3x)^(1/3x)]^[lim(x→0) (3/x) * 3/x]
= e^lim(x→0) 9
= e^9