Answer :
18-11=7 to find out how much halve the water weight
then subtract 7 from 11 11-7=4
so the emtpy bucket weighs 4 kg
[tex]x-weights \ the \ bucket \\ y-weights \ the \ water \\\\ x+y=18 =>\boxed{x=18-y} \\ x+\frac{y}{2}=11 \\\\ 18^{(2}-y^{(2}+\frac{y}{2}=11^{(2} \\\\ 36-2y+y=22 \\\\ 36-y=22 \\\\ -y=22-36 \\\\ -y=-14 \\\\ \boxed{y=14 kg} \\\\ x=18-14 \\\\ \boxed{x=4kg}[/tex]