Algebra Problem?

___2x² - 4xy + y²
__- 6x² - 9xy - y²
____x² + xy - 6y²
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- 3x² - 12 xy - 6 y²
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(2x^2 - 4xy + y^2) + (-6x^2 - 9xy - y^2) + (x^2 + xy - 6y^2)
= 2x^2 - 4xy + y^2 - 6x^2 - 9xy - y^2 + x^2 + xy - 6y^2
= 2x^2 - 6x^2 + x^2 - 4xy - 9xy + xy + y^2 - y^2 - 6y^2
= -4x^2 + x^2 - 13xy + xy - 6y^2
= -3x^2 - 12xy - 6y^2
= -3(x^2 + 4xy + 2y^2)

(2x^2 - 4xy + y^2) + ( -6x^2 - 9xy - y^2) + (x^2 + xy - 6y^2) =

Remove parentheses:
2x^2 - 4xy + y^2 + -6x^2 - 9xy - y^2 + x^2 + xy - 6y^2 =

Group like factors together:
(2x^2-6x^2+x^2) + (- 4xy- 9xy+ xy) + (y^2- y^2- 6y^2) =

Add:
-3x^2 - 12xy - 6y^2

Simplify
-3(x^2 + 4xy + 2y^2)

2x^2 -4xy +y^2-6x^2+9xy+y^2+x^2+xy-6y^2
(2x^2-6x^2+x^2) + (-4xy+9xy+xy) + (y^2+y^2-6y^2)
-3x^2+6xy-4y^2

(2x^2 - 4xy + y^2) + ( -6x^2 - 9xy - y^2) + (x^2 + xy - 6y^2)= -3x^2-12xy-6y^2
= -3(x^2+4xy+2y^2)

It will be easier if you organize the term together:
(2x^2 - 6x^2 + x^2) + (-4xy - 9xy + xy) + (y^2 - y^2 - 6y^2)
(-3x^2) + (-12xy) + (-6y^2)
--3x^2 - 12xy - 6y^2
-3(x^2 + 4xy + 2y^2)

-3x^2-12xy-6y^2

-3x^2 - 12xy - 6y^2
x(-3x - 12y) - 6y^2