We will be using e^x= sum_{n=0}^{infty}x^n/(n!)ex=∞∑n=0xnn!
Taking e^{3t} = 1 + 3t+(3t)^2/2+(3t)^3/6+... and substituting lim_{t->0}(e^{3t}-1)/t = lim_{t->0}((1+ 3t+(3t)^2/2+(3t)^3/6+...-1)/t) lim_{t->0}(e^{3t}-1)/t =lim_{t->0}(t((3+(3t)/2+(3t)^2/6+...))/t)=3