Since subtracting is the same as addition of the oppositie, just putting a negative symbol is easier because you are only working with negative numbers, instead of one negative and one positive.
(I made it addition ti make it easier, why, because if there’s a problem that doesn’t make sense right away make it addition, to make it addition just make the signs opposite, Ex: -3-5, we keep -3 and make the negative sign before the 5 into addition and now to make that equal we turn the now positive 5 into negative 5 so final result is -3+-5 which is much easier and you’ll get -8.