1, water depth:

5×5×5÷(5×2.5)

= 125÷ 12.5

= 10

That is, the water depth can reach 10dm.

2. The length is less than 30 units. Personally, I think 3dm is more suitable.

Rising water:

3× 1× 10×0.3÷(2×2)

=9÷4

=2.25

That is, the water level rises by 2.25dm.