A rectangular tank measuring 75 cm by 54 cm by 30 cm was to be filled with water by two taps, Y and Z. Tap Y which fills the tank at a rate of 6 ℓ per minute was first turned on for 3 minutes before Tap Z was turned on as well. If the tank was filled to the brim in a total of 6 minutes from the time when Tap Y was first turned on, what is the rate at which Tap Z fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 75 x 54 x 30
= 121500 cm³ 

1 ℓ = 1000 cm³ 
6 ℓ = 6000 cm³ 

Volume of water filled by Tap Y
= 6000 x 6
= 36000 cm³

Volume of water filled by Tap Z
= 121500 - 36000
= 85500 cm³ 

Rate in which Tap Z fills the tank
= 85500 ÷ 3
28500 mℓ/min
= 28.5 ℓ/min
≈ 28.5 ℓ/min (Correct to 1 decimal place)

Answer(s): 28.5 ℓ/min