Pieces of a Limit

Calculus Level 2

If the limit

$\lim _{ x\rightarrow 0 }{ \left( \frac { \sin { 2x } }{ { x }^{ 3 } } +a+\frac { b }{ { { x }^{ 2 } } } \right) } =0$

is true for constants $a$ and $b$ , then what is the value of $3a+b?$