Explanation:
we don't see a specific number line. but since it is a number line, it is a number line. as such it is counting numbers, and it has just 2 possibilities to go : left and right.
I assume the unit size is 1 (so, we are counting integer units). if it is counting fractions (like ½), then please adapt my answer accordingly.
remember, the request is to go 4 units to the left (minus) and 4 units to the right (plus).
so, our starting point on that number line is -2.
we can go the required 4 units to the left (further into the negative "territory", the negative direction) and get -2 - 4 = -6.
and we can go 4 units to the right (positive direction) and get -2 + 4 = +2