The water cycle is the process when water circulates from the oceans on the Earth, the atmosphere, land, this also involves rainfall and snow, sewers in rivers and streams, and then it returns to the atmosphere by evaporation and transpiration. Humans impact the water cycle by irrigation, urbanization, deforestation, and storing water in reservoirs.
The Gravitational spring energy(Us) is equal to 1/2kx^2. So we have x as .2 m and Us as 4 N. So 4 N = 1/2 * k * .2^2. So now we solve for K and get 200 N/m.