When an ice box is packed with 25 identical bottles of soda, it has a mass of 14.25 kg. When the ice box is packed with 30 identical packets of coffee, it has a mass of 6.9 kg. A bottle of soda weighs 330 g more than a packet of coffee. What is the mass of the empty ice box in kg?
1000 g = 1 kg
330 g = 330 ÷ 1000 = 0.33 kg

Mass of 1 packet of coffee = 1 P
Mass of 1 bottle of soda = 1 P + 0.33

Mass of 30 packets of coffee = 30 P
Mass of 25 bottles of soda = 25(1 P + 0.33) = 25 P + 8.25 

Ice Box + 25 P = 14.25 - 8.25 = 6
Ice Box + 25 P = 6 --- (1)

Ice Box + 30 P = 6.9 --- (2)

(2) - (1)
30 P - 25 P = 6.9 - 6 
5 P = 0.9

1 P = 0.9 ÷ 5 = 0.18

25 P = 25 x 0.18 = 4.5

Mass of the empty ice box
= 6 - 4.5
= 1.5 kg

Answer(s): 1.5 kg