A rectangular tank measuring 90 cm by 59 cm by 21 cm was to be filled with water by two taps, L and M. Tap L which fills the tank at a rate of 9 ℓ per minute was first turned on for 2 minutes before Tap M was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap L was first turned on, what is the rate at which Tap M fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 90 x 59 x 21
= 111510 cm³ 

1 ℓ = 1000 cm³ 
9 ℓ = 9000 cm³ 

Volume of water filled by Tap L
= 9000 x 7
= 63000 cm³

Volume of water filled by Tap M
= 111510 - 63000
= 48510 cm³ 

Rate in which Tap M fills the tank
= 48510 ÷ 5
9702 mℓ/min
= 9.702 ℓ/min
≈ 9.7 ℓ/min (Correct to 1 decimal place)

Answer(s): 9.7 ℓ/min