The total mass of 2 tanks and 3 boxes was 14.9 kg.
The total mass of 5 tanks and 5 boxes was 29 kg.

1. What is the mass of 1 tank and 1 box?
2. What is the mass of 8 boxes?
3. How much less is the mass of 1 box than 1 tank?

(a)
2 tanks + 3 boxes = 14.9 --- (1)
5 tanks + 5 boxes = 29 --- (2)

(2) _{÷ 5}
1 tank + 1 box = 5.8 --- (3)

Mass of 1 tank and 1 box = 5.8 kg

(b)
(3) x 2
2 tanks + 2 boxes = 2 x 5.8
2 tanks + 2 boxes = 11.6 --- (4)

(1) - (4)
(2 tanks + 3 tanks) - (2 tanks + 2 tanks) = 14.9 - 11.6
2 tanks - 2 tanks + 3 boxes - 2 boxes = 3.3

1 box = 3.3

8 boxes = 3.3 x 8 = 26.4

Mass of 8 boxes = 26.4 kg

(c)
Substitute 1 box = 3.3 into (3).
1 tank + 1 box = 5.8
1 tank + 3.3 = 5.8
1 tank = 5.8 - 3.3 = 2.5

Mass of 1 tank = 2.5 kg

Mass of 1 tank less than 1 box
= 3.3 - 2.5
= 0.8 kg

Answer(s): (a) 5.8 kg; (b) 26.4 kg; (c) 0.8 kg