1.

Because the volume is constant,

The volume of cubic iron block =80*80*80=5 12000 cubic centimeters.

The length of a cuboid is 512000/20 = 25600 cm = 256 m.

2.

It is equivalent to an increase of 30 cubic decimeters of water.

Height increase = 30/20 * 15 = 0. 1 decimeter.