Question

how do you know when to add or subtract negative positive numbers in equations?

Answer 1

I think this is what you are talking about an example like 2x+7=21 then you would subtract 7 on both sides the 7 on the left cancels and you end up with 2x= 14 divide by 2 on both sides the 2 on the left cancels out and your answer is x= 7. If it said something like 2x-7=21 then you would add 7 on both sides and continue the problem