X and Y are continuous random variables with joint pdf fxy

X and Y are continuous random variables with joint p.d.f. f(x,y) = c(1 + x + y)

A) find E(X + Y)

B) find Cov(X,Y)

I could use some helping finding the answer here. I managed to get one however my classmates found a different answer

I forgot to mention but the steps would be extremelly helpful. Thanks