The figure is not drawn to scale. Sabrina poured some water into Tank B and Tank C until the water levels in both tanks were the same. She found out that the total amount of water in both tanks was 42000 mℓ. She then poured another 1200 mℓ of water into Tank B to fill it to the brim. What was the height of Tank B?
Base area of Tank B
= 40 x 10
= 400 cm²

Height of 1200 mℓ of water in Tank B 
= 1200 ÷ 400
= 3 cm

Base area of Tank C
= 40 x 20 
= 800 cm²

Combined base areas of Tank B and Tank C
= 400 + 800
= 1200 cm²

Height of 42000 mℓ of water if based on the combined areas of Tank B and Tank C
= 42000 ÷ 1200
= 35 cm

Height of Tank B
= 35 + 3
= 38 cm

Answer(s): 38 cm