Intermediate Algebra (6th Edition)

12$x^{2}$y - 7xy + 3
(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