Add Op Property of Subtracting

Integers have been kicking my butt all summer. Then Mr.B as a desperate attempt to save me he showed me this method this was the first time I heard it when I was listening. He claims that he has showed me this method numerous times. I still won't believe him. If you have a problem like 18- (-24) you change the problem to an addition problem so it would be then 18+24=42 That easy!