Question

find arithmetic means between 12 and 16

Answer 1

Here is your answer 14

Answer 2

have two numbers at the ends, 12 and -16. When you insert 3 arithmetic means between them, you will have 4 intervals/segments between -16 and 12. The full length of the segment [-16,12] is 12 - (-16) = 12 + 16 = 28. Hence, the length of each smallest interval/segment between the neighbor values
will be = 7. So, your sequense is -16, -16+7 = -9, -9+7 = -2, -2+7 = 5 and 5 +7 = 12.