Using the inverse square law of radiation, what Geiger counter reading would you get for a radioactive material when you are 3 feet from the source ( assuming an initial reading of 6300 R at a distance of 1 foot from the source)?

Do you know what the term "inverse square" means? If you increase the distance by a factor x, the intensity of radiation is changed by the factor 1/x^2. So, given the radiation measurement at a distance of 1 foot, what happens to the intensity of radiation if you move to a position 3 times further away?