To get 3 5/6 - 4 5/12, you would have to get the denominators even. So 12 is the lowest, so lets use that.
3 5/6 - 4 5/12
3 10/12 - 4 5/12
3-4= -1
10-5= 5
Now, you have a -1 and a + 5/12, to do this you have to turn -1 into -12/12
-12/12 + 5/12 = -7/12
Your answer is -7/12
Hope this helped!