Answer
Interval between $[20000, 100000]$
$20,000\leq d\leq 100,000$
Work Step by Step
To calculate the distance range we have to take key points of possible maximum and minimum force and find the maximum and minimum value of distance in this range. So we have:
$0.0004=\frac{4,000,000}{d^2}$
$d_1=\sqrt{\frac{4,000,000}{0.0004}}=\sqrt{10,000,000,000}=100,000km$
$0.01=\frac{4,000,000}{d^2}$
$d_2=\sqrt{\frac{4,000,000}{0.01}}=\sqrt{400,000,000}=20,000km$
