The total mass of 5 tanks and 6 boxes was 20.9 kg.
The total mass of 4 tanks and 4 boxes was 14.8 kg.

1. What is the mass of 1 tank and 1 box?
2. What is the mass of 10 boxes?
3. How much less is the mass of 1 box than 1 tank?

(a)
5 tanks + 6 boxes = 20.9 --- (1)
4 tanks + 4 boxes = 14.8 --- (2)

(2) _{÷ 4}
1 tank + 1 box = 3.7 --- (3)

Mass of 1 tank and 1 box = 3.7 kg

(b)
(3) x 5
5 tanks + 5 boxes = 5 x 3.7
5 tanks + 5 boxes = 18.5 --- (4)

(1) - (4)
(5 tanks + 6 tanks) - (5 tanks + 5 tanks) = 20.9 - 18.5
5 tanks - 5 tanks + 6 boxes - 5 boxes = 2.4

1 box = 2.4

10 boxes = 2.4 x 10 = 24

Mass of 10 boxes = 24 kg

(c)
Substitute 1 box = 2.4 into (3).
1 tank + 1 box = 3.7
1 tank + 2.4 = 3.7
1 tank = 3.7 - 2.4 = 1.3

Mass of 1 tank = 1.3 kg

Mass of 1 tank less than 1 box
= 2.4 - 1.3
= 1.1 kg

Answer(s): (a) 3.7 kg; (b) 24 kg; (c) 1.1 kg