About how much pressure do the feet of a 6000 kg elephant exert on the ground assuming each foot has an area of 0.10 square meter

As you know, the Pressure is calculated by: force divided by area. 
Therefore, plugging in our known values:
Force is equal to 6000Kg then covert this to Newtons = 6000 kg x 9.81 N = 58680

Area is 4*(.1m^2) = .4m^2

Pressure: 58680 N / .4 m^2  = 150,000 N/m^2

i believe the answer is a hope it and is correct

speed of light in vacuum is 300,000 km/s

speed of light in other mediums is given by the expression v = c/n, where c is the speed of light in vacuum and n is the refractive index of medium.

for the first medium v = 200,000 km/s

  so, refractive index of medium = 300000/200000 = 1.5

    1.5 refractive index is usually for glass. so first medium is glass.

for the second medium v = 250,00 km/s

so, refractive index of medium = 300000/250000 = 1.2

    1.2 refractive index is usually for water. so second medium is water.

for the third medium v = 0 km/s

so, refractive index of medium = 300000/0 = ∞

    ∞ refractive index is usually for opaque mediums. so third medium is opaque medium.