3. In the expansion of $(-x y+2 x+3 y-6)^{6}$, the coefficient of $x^{4} y^{3}$ is $\qquad$ .(Answer with a specific number)
Solve
$(-x y+2 x+3 y-6)^{6}=(x-3)^{6}(y-2)^{6}$, so the coefficient of $x^{4} y^{3}$ is $C_{6}^{4}(-3)^{2} \cdot C_{6}^{3}(-2)^{3}=-72 \times 15 \times 20=-21600$