The figure shows a tank made up of 3 sections. Cuboid P with a square base of side 14 cm and height 21 cm. Cube Q with a side of 11 cm. Cuboid R that is 76 cm by 25 cm by 44 cm. Water from a tap above flows down at a rate of 3.1 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 62 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of Q
= 11 x 11 x 11
= 1331 cm³ 

Volume of R
= 76 x 25 x 44
= 83600 cm³ 

1 ℓ = 1000 cm³ 
3.1 ℓ = 3100 cm³ 

Net increase in volume per minute
= 3100 - 1000
= 2100 cm³/min

Height of P to be filled with water
= 62 - (44 + 11)
= 7 cm

Volume of water in P
= 14 x 14 x 7
= 1372 cm³ 

Volume of water in R, Q and part of P
= 83600 + 1331 + 1372
= 86303 cm³ 

Time taken to reach height
= 86303 ÷ 2100
≈ 41 min (Correct to nearest whole number)

Answer(s): 41 min