Hello,

It's a Gamma, but I think it's rather (3,1) than (2,1) (I checked it in wikipedia )

You're correct to say that P(-5<X<4)=P(0<X<4)

You can even say that it's P(X<4), where X follows

So you're looking for the value of the cumulative density function of Gamma(3,1) :

Look here : Gamma distribution - Wikipedia, the free encyclopedia