Answer:
P = 125/1296
Step-by-step explanation:
P = Number of ways of getting only 4 at the last trial / Total number of ways
Number of ways of getting only 4 at the last trial = 5 * 5 * 5 * 1 = 125
(for the first three trials, all but 4 is permissible (6 - 1 = 5 ways), and
for the last trial, only 4 is permissible (1 way)).
Total number of ways = 6 * 6 * 6 * 6 = 1296
P = 125/1296