The mean is the average. Mode is a number that appears the most.
The mean is 12, with 5 numbers, this means the total of the numbers need to sum to 12 x 5 = 60
The mode is 15, so it needs to be listed at least 2 times.
a, b, c, 15, 15
15 + 15 = 30
30 is half of 60, so the other 3 numbers need to sum to 30
Pick any 3 numbers that will sum to 30:
5 + 12 + 13 = 5 numbers can be: 5 , 12, 13, 15, 15