What number must be added to 15,-6, and 12 to have a mean of 5? Explain.

You need to add a - 1

We can find this by setting up the equation like so

x + (-6) + 12 + 15 / 4 = 5

x + 21 = 20

x = 20 - 21

x = - 1

Now if we insert - 1 where x is located in the equation, you will get a means of 5