The total mass of 4 boxes and 5 tanks was 33.5 kg.
The total mass of 5 boxes and 5 tanks was 36 kg.

1. What is the mass of 1 box and 1 tank?
2. What is the mass of 6 tanks?
3. How much less is the mass of 1 tank than 1 box?

(a)
4 boxes + 5 tanks = 33.5 --- (1)
5 boxes + 5 tanks = 36 --- (2)

(2) _{÷ 5}
1 box + 1 tank = 7.2 --- (3)

Mass of 1 box and 1 tank = 7.2 kg

(b)
(3) x 4
4 boxes + 4 tanks = 4 x 7.2
4 boxes + 4 tanks = 28.8 --- (4)

(1) - (4)
(4 boxes + 5 tanks) - (4 boxes + 4 tanks) = 33.5 - 28.8
4 boxes - 4 boxes + 5 tanks - 4 tanks = 4.7

1 tank = 4.7

6 tanks = 4.7 x 6 = 28.2

Mass of 6 tanks = 28.2 kg

(c)
Substitute 1 tank = 4.7 into (3).
1 box + 1 tank = 7.2
1 box + 4.7 = 7.2
1 box = 7.2 - 4.7 = 2.5

Mass of 1 box = 2.5 kg

Mass of 1 box less than 1 tank
= 4.7 - 2.5
= 2.2 kg

Answer(s): (a) 7.2 kg; (b) 28.2 kg; (c) 2.2 kg