Hello,

E(X1+X2)=E(X1)+E(X2)

For the variance :

var(X1+X2)=var(X1)+var(X2)+2 cov(X1,X2)

If X1 and X2 are independent, then cov(X1,X2)=0

After that, you have several other means, using probability density functions, moment generating functions, etc... But I don't know what you can use...