The figure is not drawn to scale. Y and Z are two containers. The base area of Y is 10 cm² while the base area of Z is 60 cm². Container Y and Z contained some water and the height of the water level in Container Y was 40 cm as shown. Dan then poured some water from Container Y into Container Z. After that, the height of the water level in both tanks became 19 cm. What was the height of the water level in Container Z at first?
Change in the water level of Container Y
= 40 - 19
= 21 cm

Volume of water poured in the Container Z
= 10 x 21
= 210 cm³ 

Height increase in Container Z
= 210 ÷ 60
= 3.5 cm

Original height of the water in Container Z
= 19 - 3.5
= 15.5 cm

Answer(s): 15.5 cm