A rectangular tank measuring 84 cm by 56 cm by 39 cm was to be filled with water by two taps, C and D. Tap C which fills the tank at a rate of 8 ℓ per minute was first turned on for 2 minutes before Tap D was turned on as well. If the tank was filled to the brim in a total of 6 minutes from the time when Tap C was first turned on, what is the rate at which Tap D fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 84 x 56 x 39
= 183456 cm
3 1 ℓ = 1000 cm
3 8 ℓ = 8000 cm
3 Volume of water filled by Tap C
= 8000 x 6
= 48000 cm
3 Volume of water filled by Tap D
= 183456 - 48000
= 135456 cm
3 Rate in which Tap D fills the tank
= 135456 ÷ 4
= 33864 cm3/min
33864 mℓ/min
= 33.864 ℓ/min
≈ 33.9 ℓ/min (Correct to 1 decimal place)
Answer(s): 33.9 ℓ/min