Put two rectangular prism into water

There are two large and small rectangular prisms 10 cm in height.

As shown in Fig. 1, a small rectangular prism is put on a large rectangular prism.

Moreover, water is contained in the tank of the rectangular prism as shown in Fig. 2.

The solid of Fig. 1 is straightly sunk to the bottom of the tank of Fig. 2 as it is.

When it is sunk when the initial depth of the water of a tank is 8 cm, the water surface will be gone up by 6 cm.

When it is sunk when the initial depth of water is 15 cm, the water surface will be gone up by 7.5 cm.

Find the base areas of two rectangular prism, respectively.

Answer