["Find total units: 5 + 3 = 8 units. Each unit = 640 / 8 = 80 seats.","Orchestra = 5 x 80 = 400. Occupied:empty = 9:1 so empty orchestra = 1/10 x 400 = 40.","Balcony = 3 x 80 = 240. Occupied:empty = 5:3 so empty balcony = 3/8 x 240 = 90. Total empty = 40 + 90 = 130."]