You roll a 6-sided die. Find the P(4).

Because all outcomes are equally weighted, the probability you are looking for is given by :-
Number of favorable eventsTotal number of events
Number of favorable events
Total number of events

In your case: 6 or Even outcome={2,4,6}
6
or Even outcome
=
{
2
,
4
,
6
}
and Outcomes={1,2,3,4,5,6}
Outcomes
=
{
1
,
2
,
3
,
4
,
5
,
6
}

Hence:

Number of favourable eventsTotal number of events=36=12