Assume that the numbers are X and Y; The sum of the two numbers is: X+Y=-12 Their difference is: X-Y=84 We can present the number X as a funsction from Y, from any of the equation. Let do that from the first: X=-12-Y Now, in order to have only one unknown we will write X in this form in the second equation: (-12-Y)-Y=84 -12-Y-Y=84 -12-2Y=84 -12-84=2Y -96=2Y Y=-96/2=-48 X=-12-Y=-12-(-48)=-12+48=36
