376+-3=?

and how do i get my couculater to subtract negative numbers

Well you could think of this like this
-376+-3, is the same as adding with negatives, instead of adding with positives, like 376+3, we are only changing the sign in front of it. So instead of it being equal to 379, -376+-3 = -379.

No because if you do the higher number minus the lower number you will get a positive. if you do it the other way around you will get a negative number