Probability pdf questions

1. The joint probability density function of X and Y is given by f(x,y)= C(y-x) e^(-y) where -y<x<y , 0<y<infinity

(a) Find the value of C
(b) Find the marginal distribution functions of X and Y
(c) Find the conditional distribution of X given Y = y

2. If X and Y have the joint pdf f X,Y(x,y)= 2(x+y) , 0<=x<=y<=1, find f Z(z), where Z= X+Y.