Volume of tank = 30cm x 18cm x 24cm

= 12960cm³

= 12.96 litres

Remaining volume to be filled = 5/8 x 12.96 litres – 3.7 litres

=4.4 litres

=4 litres 400 millilitres

Answer: 4 litres 400 millilitres

Total volume of tank -> 30 × 18 × 24 = 12960 ml

At first, (1 – ³/₈) = ⁵/₈ of it was empty

Volume of empty space -> ⁵/₈ × 12960 = 8100 ml

After 3.7 l of water poured in,

Volume of empty space -> 8100 – 3700 = 4400 ml

Answer: 4 litre 400 ml