The relation between the water temperature and depth of the water is inversely proportional.
Let water temperature be t and depth of water is d.
The relation is written as
[tex]t.d=k[/tex]here k is the constant of proportionality .
For the depth of water 1000 m , the temperature is 9° Celsius.
[tex]1000.9=k[/tex][tex]k=9000.[/tex]Thus the value of constant of proportionality k is 9000.
For depth of 800 meters , the temperature of water is
[tex]t.800=9000[/tex][tex]t=\frac{9000}{800}[/tex][tex]t=11.25^{\circ}C[/tex]Therefore, the temperature of water with depth of 800 meters is 11.25 degree Celsius.