Probability: mutually exclusive events

Hi!

So i don't know why but i am totally bugging on this problem:

"An experiment results in one of three mutually exclusive events A,B and C. It is knows that p(A)=.30, p(B)=.55 and p(C)=.15.

Find each of the following probabilities:

a - p(a u b)

b - p(a n b)

c - p(a|b)

d - p(b u c) "

so i would know how to find b-, c- and d- but i can't get started with a-.

they say it's mutually exclusive, but does it mean that p(a n b n c)=0 or that p(a n b)= 0 and p(a n c)=0 and p(b n c)= 0 ?

I am confused! Thanks..