When an ice box is packed with 15 identical bottles of soda, it has a mass of 12.15 kg. When the ice box is packed with 30 identical packets of coffee, it has a mass of 5.1 kg. A bottle of soda weighs 580 g more than a packet of coffee. What is the mass of the empty ice box in kg?
1000 g = 1 kg
580 g = 580 ÷ 1000 = 0.58 kg

Mass of 1 packet of coffee = 1 P
Mass of 1 bottle of soda = 1 P + 0.58

Mass of 30 packets of coffee = 30 P
Mass of 15 bottles of soda = 15(1 P + 0.58) = 15 P + 8.7 

Ice Box + 15 P = 12.15 - 8.7 = 3.45
Ice Box + 15 P = 3.45 --- (1)

Ice Box + 30 P = 5.1 --- (2)

(2) - (1)
30 P - 15 P = 5.1 - 3.45 
15 P = 1.65

1 P = 1.65 ÷ 15 = 0.11

15 P = 15 x 0.11 = 1.65

Mass of the empty ice box
= 3.45 - 1.65
= 1.8 kg

Answer(s): 1.8 kg