Total seats = 640. Orchestra : Balcony = 5 : 3.<br><br>
[[model:questions/solutions/q10510.png]]<br><br>
Total units = 5 + 3 = 8 units<br>
&bull; 8 units → 640<br>
&bull; 1 unit → 640 ÷ 8 = 80<br>
&bull; Orchestra = 5 units = 5 × 80 = 400<br>
&bull; Balcony = 3 units = 3 × 80 = 240<br><br>
Now find empty seats in each section:<br>
Orchestra &mdash; occupied : empty = 9 : 1, so empty orchestra = \( \frac{1}{10} \) × 400 = 40<br>
Balcony &mdash; occupied : empty = 5 : 3, so empty balcony = \( \frac{3}{8} \) × 240 = 90<br><br>
Total empty seats = 40 + 90 = 130<br>
Check: Occupied orchestra = 360, occupied balcony = 150. 40 + 90 + 360 + 150 = 640. ✓<br><br>
Final Answer: 130