For the given joint probability density f(x,y) = 2 for x>0, y>0, x+y<1; 0 elsewhere: find P(X+Y>0.75).

I got that the limits of the density function itself are {x,0,1} and {y,0,1-x}. For this specifc probability though, x+y<1 AND x+y>0.75, right? Possibly it is {x,0.75,1}, {y,0,1-x} ? I don't think so though, because that assumes x is the greater number here.