Use the volume formula: Volume = Length × Width × Height.<br><br>
&bull; 21 × Width × 8 = 2016<br>
&bull; 168 × Width = 2016 (since 21 × 8 = 168)<br>
&bull; Width = 2016 ÷ 168 = 12 cm<br><br>
Final Answer: 12 cm