How do you subtract a integer from another integer without using a number line or counters

This is how I do it. If it is a negative minus a negative, I combine the two - signs to make it an addition problem. Ex. - 3 - - 4 makes - 3+4. The answer would be one.

If it is a negative plus a negative, keep the sign on the greater number and take away the sign the smaller number. Ex. - 7 + (-9). Keep the sign on the 9. - 7 - 9. The answer would be - 16.