Final answer:
The set of all positive integers greater than 12 and less than or equal to 6 is an empty set.
Step-by-step explanation:
(d) The set of all positive integers greater than 12 and less than or equal to 6 is an empty set. This is because there are no positive integers that are simultaneously greater than 12 and less than or equal to 6.
Therefore, the roster method for this set is {}.