A rectangular tank measuring 77 cm by 56 cm by 30 cm was to be filled with water by two taps, W and X. Tap W which fills the tank at a rate of 9 ℓ per minute was first turned on for 2 minutes before Tap X was turned on as well. If the tank was filled to the brim in a total of 6 minutes from the time when Tap W was first turned on, what is the rate at which Tap X fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 77 x 56 x 30
= 129360 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap W
= 9000 x 6
= 54000 cm
3 Volume of water filled by Tap X
= 129360 - 54000
= 75360 cm
3 Rate in which Tap X fills the tank
= 75360 ÷ 4
= 18840 cm3/min
18840 mℓ/min
= 18.84 ℓ/min
≈ 18.8 ℓ/min (Correct to 1 decimal place)
Answer(s): 18.8 ℓ/min