Answer:
the mode is 12
Explanation:
Arrange the numbers in order : 1 , 3, 6, 6, 9, 9, 12, 12, 12, 12, 12, 15, 15, 15, 15
Then count how many numbers that appears the most, so the number that appears the most is 12, therefore, the mode in the data set is 12 .