Answer:
It is 6mn² if you want to know the greatest common factor.
Explanation:
Let me start with the coefficients. Since 6 can divide all coefficients, we should pick 6.
For the variables, the least power of m found in the expression is m¹ or simply m.
The least power of n found in the expression is n². Wrapping this up, you get 6mn².
But the expression has many common factors.
e.g. 2, 3, 6, m, n, n², . . .
You can also say -2, -3, -6, -m, -n, -n².
Generally, you may have many common factors, but you will have only one greatest common factor.