Find the three arithmetic means in this sequence. 12 __ __ __ 40

To answer this question first you have to count the difference between the highest number with the lowest number.
In this case, the difference is: 40-12=28

After that, you need to determine the leaps in the sequence. In this case, there are 4 leaps.  
After that divide the difference with the leaps : 28:4=7
Therefore the sequence will be 12 , 19, 26, 33, 40