Prove that $\displaystyle 3^n \geq 3n$.

If $\displaystyle n=1$, then $\displaystyle 3^1=3(1)$. Clearly, this is true.

Assume $\displaystyle n=k$ and $\displaystyle 3^k \geq 3k$.

If $\displaystyle n=k+1$, then $\displaystyle 3^{k+1}=3^k 3$

I am stuck here. Can someone explain how to show $\displaystyle 3^{k+1} \geq 3(k+1)$? Thank you.