The figure shows a tank made up of 3 sections. Cuboid T with a square base of side 9 cm and height 35 cm. Cube U with a side of 19 cm. Cuboid V that is 61 cm by 12 cm by 40 cm. Water from a tap above flows down at a rate of 2.7 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 tank to a height of 66 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of U
= 19 x 19 x 19
= 6859 cm³ 

Volume of V
= 61 x 12 x 40
= 29280 cm³ 

2 ℓ = 2000 cm³ 
2.7 ℓ = 2700 cm³ 

Net increase in volume per minute
= 2700 - 2000
= 700 cm³/min

Height of T to be filled with water
= 66 - (40 + 19)
= 7 cm

Volume of water in T
= 9 x 9 x 7
= 567 cm³ 

Volume of water in V, U and part of T
= 29280 + 6859 + 567
= 36706 cm³ 

Time taken to reach height
= 36706 ÷ 700
≈ 52 min (Correct to nearest whole number)

Answer(s): 52 min