Looking at the factors above, the common ones are 1, 2, 3, 4, 6, 9, 12, 18, and 36. But... considering we are looking for the "greatest" common factor, our highest number out of the listed ones is 36, making it the greatest common factor of 72 and 36.
So, draw your line from the equation, and then lightly shade the left and ride side. That middle side is where there is no solutions for -3 ≤ x ≤ -5 for y = 2x - 5.