Answer
12$x^{2}$y - 7xy + 3
Work Step by Step
(3$x^{2}$y - 7xy - 4) + (9$x^{2}$y + x) - (x - 7)
= 3$x^{2}$y - 7xy - 4 + 9$x^{2}$y + x - x + 7
= (3$x^{2}$y+ 9$x^{2}$y) - 7xy + (x - x) + (7 - 4)
= 12$x^{2}$y - 7xy + 3
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