If 
and 
are mutually independent, then 
and 
.
If and 
are independent, then 
. Ditto for and .
The inclusion/exclusion principle says that
Since and are mutually exclusive, their intersection is the empty set. It then follows that 
also is the empty set, so the last probability is also 0.
Plug in what we know:
If
The inclusion/exclusion principle says that
Since
Plug in what we know:
