# Convolution of Discrete Variable and Random Variables , Need Urgent Help

GROUPS:
 K=Z-(X+Y)Z is any dicrete value . I applied convolution for PDF of two exponential random variables (X and Y). Which is like that here. Now I need to compute PDF and expected value of K ? I learned that I can do it with delta function but I could not manage it . I will be very appreciate if anyone can help me .