Pretty simple question:

f(x,y) = {2 if 0 <= x <= y <= 1 , 0 elsewhere}

How do I compute P(X<2Y) ?

Similarly, if I'm given the following CDF,

F(x,y) = (1-exp(-x^2))(1-exp(-y^2)) on {x,y>0}

How would I compute P(X<2Y) here?

Thanks in advance for your help!