Respuesta :

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}