Proving this binomial identity $\sum_{k=0}^n {n+k \choose k} \frac{1}{2^{k}}= 2^{n}$

Question

A teacher gave this as a homework question, and I have tried but haven't been able to arrive at a solution.
$\sum_{k=0}^n {n+k \choose k} \frac{1}{2^{k}}= 2^{n}$
Could someone prove it, or at least point me in the right direction ?