In the sample space, there are 216 outcomes, with each element of the sample space having three entries and taking the form
Considering the event, E: 4 appears on the third toss
Now the event, F: 6 and 5 appears respectively on the first two tosses
We get the common sample space of both,
So,
Now, we know that by definition of conditional probability,
Now by substituting the values we get