At what depth below the surface of the earth, acceleration due to gravity is will be half its value 1600 km above the surface of the earth?

Radius of earth R=6400km⇒h=R4Acceleration due to gravity at a height hgh=gRR+h2=gRR+R42=1625gAt depth d, value of acceleration due to gravitygd=12gh      (According to problem)⇒ gd=121625g⇒g1−dR=121625gBy solving we get d=4.3×106m