A bacteria culture doubles every hour. If there are 15 000 bacteria now, how many bacteria were there 6 hours ago?

234.375 or about 234. 
Half it several times to get the answer.
15000/2=7500 (1 hour ago)
7500/2= 3750 (2 hours ago)
3750/2= 1875 (3 hours ago)
1875/2=937.5 (4 hours ago)
937.5/2= 468.75 (5 hours ago)
468.75/2= 234.375 (6 hours ago)
Therefore, there were 234.375 or about 234 bacteria 6 hours ago.