已知A=(2x+1)(x-1)-x(1-3y),B=-x^2-xy-1,且3A+6B的值与x无关,求y的值

3A+6B
=3(2x+1)(x-1)-x(1-3y)+6(-x^2-xy-1)
=6x^2-3x-3-x+3xy-6x^2-6xy-6
=-4x-3xy-9
=-(4+3y)x-9
值与x无关则x的系数为0
所以-(4+3y)=0
3y=-4
y=-4/3