The figure shows a tank made up of 3 sections. Cuboid S with a square base of side 25 cm and height 32 cm. Cube T with a side of 17 cm. Cuboid U that is 69 cm by 30 cm by 43 cm. Water from a tap above flows down at a rate of 2.2 litres per minute while water is drained out from the bottom at a rate of 1 litre per minute. How long did it take to fill up the tank to a height of 67 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of T
= 17 x 17 x 17
= 4913 cm³ 

Volume of U
= 69 x 30 x 43
= 89010 cm³ 

1 ℓ = 1000 cm³ 
2.2 ℓ = 2200 cm³ 

Net increase in volume per minute
= 2200 - 1000
= 1200 cm³/min

Height of S to be filled with water
= 67 - (43 + 17)
= 7 cm

Volume of water in S
= 25 x 25 x 7
= 4375 cm³ 

Volume of water in U, T and part of S
= 89010 + 4913 + 4375
= 98298 cm³ 

Time taken to reach height
= 98298 ÷ 1200
≈ 82 min (Correct to nearest whole number)

Answer(s): 82 min