Volume of container = 5 cm × 4 cm × 20 cm = 400 cm&sup3;.<br><br>
&bull; The container is filled to \( \frac{9}{10} \) of its height.<br>
&bull; Volume of detergent = \( \frac{9}{10} \) × 400 = 360 cm&sup3;.<br><br>
Final Answer: 360 cm&sup3;