Inverse Square law of Radiation

The best means of personal protection from radiation for emergency responders is the implementation of three basic principles: time, distance and shielding. Please show your work when answering the following questions: 

a. 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 (assume an initial reading of 6300 R at a distance of 1 foot from the source)? 

b. Dr. Brown has a radioisotope source containing 1.2 x 106 (also written as 1.2E+06) atoms of Plutonium-238 in 1985, how many atoms will remain in 352 years? 

c. How many protons and neutrons are present in the plutonium-238 nucleus