Explain how you can add on to find the differennce 727-685

You can do something call KCC. It means keep the sign of 727 (which is positive) and change the - (Subtraction sign) to + (addition sign) and change again the positive 685 (685) to a negetive 685 (-685) so now the new equation is 727 + (-685) = 42 and 727-685=42