In order to find this, first find the greatest common factor of the coefficients. Since 3 goes in evenly to both 15 and -18, then we know that it is a common factor.
From there we need to find the number of x's. Since the first term only has 2 x's and the second has 3, we take the lowest number. (x^2)
And since the first term has 3 y's and the second has just 1, we take the lowest number (y).
