Answer :
Bacteria B started with 3000 bacteria.
Bacteria B doubles every hour.
In three hours, the amount of Bacteria A will be greater than the amount of Bacteria B.
Bacteria A: 
x=0 , y = 1000
x=1 , y = 3000
x=2 , y = 9000
x=3 , y = 27000
Bacteria A: 
x=0 , y = 3000
x=1 , y = 6000
x=2 , y = 12000
x=3 , y = 24000
From this table we can see that Bacteria B started with 3000 bacteria.
Bacteria B doubles every hour, 3000, 6000, 12000, 24000
In 3 hours , Bacteria A = 27000 and Bacteria B = 24000
So,In three hours, the amount of Bacteria A will be greater than the amount of Bacteria B.