Asix-sided fair die is rolled 4 times in a row. the probability of getting a 4 only on the last trial is

The probability of getting a 4 only on the last trial is  

Explanation:

When a die rolled single time, total number of favorable outcome is given as  {1,2,3,4,5,6}

when the die is rolled single time Probability of having  4 on die is

and if die is roll and Probability of not having  4 is

Now, when die Rolled 4 times in a row, then probability of having  4 only on last trial is