A rectangular tank measuring 87 cm by 57 cm by 26 cm was to be filled with water by two taps, Q and R. Tap Q which fills the tank at a rate of 8 ℓ per minute was first turned on for 4 minutes before Tap R was turned on as well. If the tank was filled to the brim in a total of 5 minutes from the time when Tap Q was first turned on, what is the rate at which Tap R fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 87 x 57 x 26
= 128934 cm³ 

1 ℓ = 1000 cm³ 
8 ℓ = 8000 cm³ 

Volume of water filled by Tap Q
= 8000 x 5
= 40000 cm³

Volume of water filled by Tap R
= 128934 - 40000
= 88934 cm³ 

Rate in which Tap R fills the tank
= 88934 ÷ 1
88934 mℓ/min
= 88.934 ℓ/min
≈ 88.9 ℓ/min (Correct to 1 decimal place)

Answer(s): 88.9 ℓ/min