15 and 12 are two factors of 180 that differ in 3 units and whose product is exactly 180. And there are no other such positive numbers. (But still there are negative: -15 and -12). Notice that I presented you the MENTAL solution. There is another way to solve the problem using equation: x*(x+3) = 180, x^2 + 3x - 180 = 0, (x-12)*(x+15) = 0, which gives the roots x = 12 and x = -15.