Assuming the earth to be a sphere of uniform mass density, a body weighed \( 300 \, \text{N} \) on the surface of earth. How much it would weigh at \( R/4 \) depth under surface of earth?
\( 300 \, \text{N} \)
\( 225 \, \text{N} \)
\( 375 \, \text{N} \)
\( 75 \, \text{N} \)