What is the mode if this numbers 12,15,8,6,7,6,6,8,8,9,3

The mode is the number that occurs a lot which in this case will be 8 and 6 and can be two numbers

The mode is the number that apears the most times in a set of data 
what you should do is list the numbers from least to greatest because it helps so the numbers are now listed as 3,6,6,6,7.8.8.8.9.12.15 as you can see  there are two modes there is 6 and 8 now you have to find the average or you can use the number in the middle of 6,8  
6+8=14/2=7
 6,7,8

31 is prime. and it’s prime factorization is just 31.