Positive and negitive numbers

This term we have been working with positive and negitve numbers. We have been working with figure it outs books to help us. these are the keys to understand positive from neitive, += positive, - = negitve. I have learnt that if you had +8 + -4 it would = -12 because the to last symbols are different and that means that the answer is going to be a negitive, but if it was like this +7- -3 it would = +10 because the last two numbers are the same so the answer will always be a positive.
In this figure it out book we have to see how many years between the eruptions of the volcanos. The number line has a zero in the middle of it, to the left of the zero it means negative to the right of the zero it means positive.