Answer :
We want to calculate distance of the object to the center of the earth for which gravitational force is equal to 0.000625 N and 0.0025 N
Note: correction in the formula given otherwise have no sense, because gravitational force is higher when distance is near to earth and weaker when object goes away, that means force and distance are inversely proportional.
So then we need to solve the given equation for these values:
F = 4000000/d^2 => d = (4000000/F)^1/2 = (4000000/0.000625)^1/2 = 80,000 km
F = 4000000/d^2 => d = (4000000/F)^1/2 = (4000000/0.0025)^1/2 = 40,000 km
So then the gravitational force is between 0.000625 N and 0.0025 N when :
40,000 <= d <= 80,000 km