A rectangular tank measuring 86 cm by 50 cm by 29 cm was to be filled with water by two taps, Y and Z. Tap Y which fills the tank at a rate of 8 ℓ per minute was first turned on for 4 minutes before Tap Z was turned on as well. If the tank was filled to the brim in a total of 7 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
= 86 x 50 x 29
= 124700 cm³ 

1 ℓ = 1000 cm³ 
8 ℓ = 8000 cm³ 

Volume of water filled by Tap Y
= 8000 x 7
= 56000 cm³

Volume of water filled by Tap Z
= 124700 - 56000
= 68700 cm³ 

Rate in which Tap Z fills the tank
= 68700 ÷ 3
22900 mℓ/min
= 22.9 ℓ/min
≈ 22.9 ℓ/min

Answer(s): 22.9 ℓ/min