help on point source calculations

[Lzjk@aol.com]

Can anyone show me how to do the following problems? or send me some good 
examples with equations. 

If the Co-60 point source had a radiation intensity of 4.2 R/hr at two feet, 
the distance at which the exposure rate would be 100 mR/hr  is ? 

What equation do I use and please give a example on how to do it.


next question

Calculate exopsure rate at 3' from a 11' long line source. The line source is 
reading an exposure rate of 600 mR/hr at 1 inch from the line.

Thanks for any help I can get.
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