Marginal Probability Mass Func

Suppose the joint probability mass function of X and Y is

P[{X=n, Y=m}] = { (e^-14) (7.14^m) (6.86^(n-m)) } / (m! (n-m)!)

where m = 0, 1, 2, ... , n; n = 0, 1, 2, ...

Please find

a) the marginal probability mass function of Y

and

b) the mean of X and Y

and lastly

c) the conditional pmf of X given Y=2.

Your help is much appreciated if you have help me any question above :)