Strange radioactivity question. plz help fast!

I know this is in the k-12 forum too but i wasnt sure if this is college level stuff or not so sorrie if this is in the wrong forum.

And im not telling u to do this for me, i just wanna know some equations and anything that wuld help.

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.

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I'm not completely familiar with this term, but if a 5.0x10^-4m^2 detector is what I think it is, the solution would simply be:

(rate of the source)*(area of the detector)/(surface of the sphere with radius 20 cm,... etc.)

In the experiment that we have to do after we do the calculations, we are going to be given a detector device which looks sorta like a large yellow calculator with a square hole on the top. Thats the part that does the detecting. You can switch the top part to have a aluminum foil covering and or some thicker metal covering. The sources we have are these small colored chips that have labels on them tellin u if their beta alpha or gamma. Hope that helps to clarify what the detector is.

As for the equation u gave out: (rate of the source)*(area of the detector)/(surface of the sphere with radius 20 cm,... etc.), what do u mean by the "surface of the sphere with radius 20 cm,... etc"??????How do u implement the distances and the value of the sources(Bq) into the equations.

Like from what i see: this is what u plug in right? : (rate of source)(5.0x10^-4m^2)/(????).

O and by the way, where or how did u derive that equation from.

wait, by surface of the sphere with radius 20 cm, do u mean surface area? Because the detector does not detect 360 degrees. By 20 cm, 50 cm, etc..., i think it means the source chip is placed 20 cm from the tip of the source. So with that in mind, does the equation change...?