x^3y^(m-1)x^(n+m)y^(2n+2)
=x^(3+n+m)y^(m-1+2n+2)
=x^(m+n+3)y^(m+2n+1)
=x^9y^9
m+n+3=9
m+2n+1=9
解得
m=4n=2
4m-3n=16-6=10
选C.