5x^{2}y + 4xy - 9x^{2}y - 4xy

We have : 5x^{2}y + 4xy - 9x^{2}y - 4xy

= 5x^{2}y - 9x^{2}y + 4xy - 4xy

= -4x^{2}y

Good

We have : 5x2y + 4xy - 9x2y - 4xy

= 5x2y - 9x2y + 4xy - 4xy

= -4x2y

Thank