You can put this solution on YOUR website! Well, I will answer your question like this -7 is not a factor of 28 factors are what number times a number will give you -7 so the factors of -7 is 1,7 and thats it and if it is the GCF (Greatest common factor) it will be 7 and if it is the LCF(Lowest common factor) it will be 1. So I hope thats enough information for you glad to help you!.