(-3y-1) – (6y-4) – (y+4)

I'm going to tell you to do it the easy way, not the stupid way;

You have y's and constants

Count them at the same time paying attention to sign changes.

This problem is:

(-3y-1) + (-1)(6y-4)+(-1) (y+4)

Now count the y's and constants and eventually add

y: -3, -6, -1

Constants: -1, 4, -4

Add the y's
-10y

Add constants

-1

-1-10y

Done, and simeple. Bet it's not the way you were taught?

The way you were taught, if I'm correct, is too error prone.