What is the sum of - 4 and - 6?

If you need to know the sum you need to add. So if you are adding two negative numbers, basicaly, you are doing subtration.

4 - 6 = - 2

So we just flip the negative 2 into a positive 2.

On a number line,

negative means go left

positive means go right

-4 means go 4 units left of zero

-6 means another 6 units left of 0

4+6=10

that means 10 total units left or - 10