Answer:
8
Explanation:
If strontium has a half-life of 3 hours and you have 64 grams of it that means every 3 hours strontium's grams will be divided by 2.
So you have 64/2 = 32 for the first half life {Time is currently at 3 hours}
32/2 = 16 for the second half life {Time is currently 6 hours}
Then you have 16/2 = 8 for the third half-life {Time is currently 9 hours}
