x2+11x+30=(x+5)(x+6); x3-4x2-21x=x(x-7)(x+3); 4x2+20x=4x(x+5).
(x3-4x2-21x)/(4x2+20x)=x(x-7)(x+3)/[4x(x+5)]=(x-7)(x+3)/[4(x+5)].
The first factor doesn't look right: 4x+12^2? Could it be 4x+12? 4x+12=4(x+3).
(4x+12)/(x2+11x+30)=4(x+3)/[(x+5)(x+6)];
So (4x+12)/(x2+11x+30)/[(x3-4x2-21x)/(4x2+20x)]=
4(x+3)/[(x+5)(x+6)] × [4(x+5)]/[(x-7)(x+3)]=
16(x+3)(x+5)/[(x+5)(x+6)(x-7)(x+3)]=
16/[(x+6)(x-7)] or 16/(x2-x-42).