BMAT 2021 chemistry

I tried to solve this without any formula but so can anyone solve this simply without any complex steps or without using complex formulas…?

Is the answer F?
I think this is a question related to half-life, so you don’t need any formula to solve.
248 → 124 → 62 → 31
It happened 3 times in 48 hours: 48/3=16h

First of all the sample is actually 224 counts per minute because 24 counts were already there before the sample placed there.
And the correct answer is D.

Oh I didn’t think that. I’m sorry.
248-24=224
31-24=7
224->112->56->28->14->7
5 times in 48 hours, so 48/5 = 9.6h

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Thanks😊 …I also did not reduced the 24 counts. In the end that’s why i was getting it wrong😶‍🌫️.