Slippery Sum!

Calculus Level 4

$\displaystyle\sum _{ r=1 }^{ \infty }{ \frac { r\left( r+1 \right) }{ { 3 }^{ r } } }$

If the summation above equals to $\frac m n$ for coprime positive integers $m,n$ , what is the value of $m+n$ ?