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we know that for variation of g with height(h),
g' = g(1- 2h/R)
and for v
ariation of g with depth(d)
g' = g(1- d/R)

According to the question,
g(1- 2h/R) = g(1- d/R)
⇒ 1- 2h/R = 1- d/R
⇒ 2h/R = d/R
⇒ 2h = d
⇒ 2h = 80 Km            
h = 40 Km (Ans.)

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