An electronic system has two components X and Y, and works if just one or both components are functioning. Their lifespan function is written as:

f(x,y) = 2^e−(x+2y), x > 0, y > 0, otherwise 0

I've calculted the marginal distributions to be:

g(x) = e^-x

h(y) = 2e^-2y

Next I'm supposed to figure out the expected lifespan for X and Y, plus the variance in lifespan for each. Would appreciate any help!