Volume of the cubical tank = 50 × 50 × 50 = 125&thinsp;000 cm&sup3; = 125 L.<br><br>
&bull; Time to empty = 125 ÷ 15 = \(\frac{25}{3} = 8\frac{1}{3}\) minutes<br>
&bull; \(\frac{1}{3}\) of a minute = 60 × \(\frac{1}{3}\) = 20 seconds<br>
&bull; Total time = 8 minutes 20 seconds<br><br>
Final Answer: 8 min 20 sec