# Who's up to the challenge? 20

Calculus Level 5

$\large \int _{ 0 }^{ \infty } { x }^{ 3 }{ e }^{ -3x }\sin { x } \, dx$

If the integral above is the form of $\dfrac ab$, where $a$ and $b$ are coprime positive integers, find $a+b$.

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