The scale factor can be found by dividing two corresponding side lengths. For instance, if you have two triangles, divide the new length of the larger or smaller triangle by the same side length of the original.
If the side length of the new was 9 and the old was 3 then the scale factor would be 9/3 = 3.
If it were flipped then the new would be 3 and the old would be 9. So the scale factor would be 3/9 = 1/3.
x+(-7) or (standard form) 
x+y=-7