Creating a formula for calculating $\sum\limits_{k=1}^n\frac k{(1+r)^k}$

Question

Can anyone help to find a formula for this?

$$\sum_{k=1}^n\frac{k}{(1+r)^k}=\frac{1}{1+r}+\frac{2}{(1+r)^2}+\frac{3}{(1+r)^3}+\cdots+\frac{n}{(1+r)^n}.$$

I cannot seem to use $\dfrac{n(n+1)}{2}$ in anyway.