The figure shows a container made up of 3 sections. Cuboid R with a square base of side 4 cm and height 39 cm. Cube S with a side of 18 cm. Cuboid T that is 75 cm by 26 cm by 40 cm. Water from a tap above flows down at a rate of 3.9 litres per minute while water is drained out from the bottom at a rate of 2 litre per minute. How long did it take to fill up the container to a height of 65 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of S
= 18 x 18 x 18
= 5832 cm³ 

Volume of T
= 75 x 26 x 40
= 78000 cm³ 

2 ℓ = 2000 cm³ 
3.9 ℓ = 3900 cm³ 

Net increase in volume per minute
= 3900 - 2000
= 1900 cm³/min

Height of R to be filled with water
= 65 - (40 + 18)
= 7 cm

Volume of water in R
= 4 x 4 x 7
= 112 cm³ 

Volume of water in T, S and part of R
= 78000 + 5832 + 112
= 83944 cm³ 

Time taken to reach height
= 83944 ÷ 1900
≈ 44 min (Correct to nearest whole number)

Answer(s): 44 min