Strange radioactivity question. plz help fast!

well, this is a strange question that i have to do a presentation on. I thought it would be easy but i cant find any information after looking through 2 major physics books and searching online. I even asked a tutor about this and still couldnt get any equations i could use. Plz dont bash me if this is the wrong forum. Just direct me to the right one then. This is the problem:
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Radioactive Emission Ranges: For a 35 becquerel (Bq) source of alpha radiation, calculate the rate of particles arriving at a 5.0x10^-4m^2 detector located 20.0 cm, 50.0 cm, 100.0cm, and 130 cm from the source. Repeat the calculations for the same detector at the same positions for a 48 Bq source, a 125 Bq source, and a 1753 Bq source.

Tabulate and graph your results on a detection rate (Bq) versus distance (cm) graph, with source activity(Bq) as an extra parameter.
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Just need an equation or equations to solve this. You don't have to solve it. Im not tryin to cheat, i just need to know where to even start with this thing. I cant find any equation that includes distance along with detection rate and area. Both books dont have anything. Am i suppose to use several equations together or wat? If anyone has any idea how this is done, plz help me.