Answer: 25 days.
Step-by-step explanation: First, to figure this out, you need to find what 8 is multiplied by to get 100. The answer is 12.5, so to double the kitten's weight, it would take 12.5 days. Now all you need to do it do that one more time. Adding another 12.5 days, the total would be 25 days. So, in 25 days, the kitten will go from 100 grams to 300 grams.