i'm a little confused as to how to go about this, so if anyone could help i'd appreciate it!
The derivation is long the standard way. It is simpler with complex analysis but I assume you do not know that method. Thus, instead of deriving it I will just mention a formula,
But what do you do if there is a constant in front of the e (there is a 3 in front)?
Rememeber any constant function can always be factored out of the integrand. Thus, you can do the problem without the 3, and when you finish multiply everything by 3.