The total mass of 4 boxes and 5 tanks was 22.2 kg.
The total mass of 6 boxes and 6 tanks was 28.2 kg.

1. What is the mass of 1 box and 1 tank?
2. What is the mass of 5 tanks?
3. How much less is the mass of 1 tank than 1 box?

(a)
4 boxes + 5 tanks = 22.2 --- (1)
6 boxes + 6 tanks = 28.2 --- (2)

(2) _{÷ 6}
1 box + 1 tank = 4.7 --- (3)

Mass of 1 box and 1 tank = 4.7 kg

(b)
(3) x 4
4 boxes + 4 tanks = 4 x 4.7
4 boxes + 4 tanks = 18.8 --- (4)

(1) - (4)
(4 boxes + 5 tanks) - (4 boxes + 4 tanks) = 22.2 - 18.8
4 boxes - 4 boxes + 5 tanks - 4 tanks = 3.4

1 tank = 3.4

5 tanks = 3.4 x 5 = 17

Mass of 5 tanks = 17 kg

(c)
Substitute 1 tank = 3.4 into (3).
1 box + 1 tank = 4.7
1 box + 3.4 = 4.7
1 box = 4.7 - 3.4 = 1.3

Mass of 1 box = 1.3 kg

Mass of 1 box less than 1 tank
= 3.4 - 1.3
= 2.1 kg

Answer(s): (a) 4.7 kg; (b) 17 kg; (c) 2.1 kg