it's asking for he greatest common factor respond asap!

Number 6 is wrong. The answer is 2x^3. Number 7 is wrong. The answer is 2x. Number 8 is wrong. The answer is 10y^2. Number 10 is wrong. The answer is 12y^2. Number 11 is wrong. The answer is 7mn. Number 12: x^5*y^2. Number 13: 6x^2. Number 14: x^2*y. Number 15: 15x. Number 16: 3x^4*y^2. Number 17: xy. Number 18: 2x^2*y^3. Number 19: 3x^2. Number 20: 3x. Number 21: 6x^4. 

I believe the answer is 25