Answer: 10 minutes.
Step-by-step explanation: Since the cells get double in every 5 minutes, so the number of bottles that will be filled in 5 minutes= 2. After another 5 minutes, these 2 bottles of cells will fill another two bottles. Now, out of these 4 bottles, one is old which was already filled with cells. So, no. of new bottles filled=3 in 10 minutes.
So, it will take 10 minutes to fill another 3 bottles of the same size.