Question

What is the sum of -4 and -6?

Answer 1

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

Answer 2

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.