Which is a factor of 6x2y + 8x2 − 30y − 40?

6x^2y + 8x^2 − 30y − 40
= 2x^2(3y + 4) - 10(3y + 4)
= (2x^2 - 10)(3y + 4)
= 2(x^2 - 5)(3y + 4)

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.