Do you have a question? Like "is this true?".

Assuming the cat is already at least 4 months old, in two months she can have a litter. we are told "number of kittens in a litter, 4 to 6" so lets take 5 as an average. She now has 5 "descendants". Two months later, now a total of 4 months, she has another litter of 5 kittens. She now has 20 "descendants". But each of the first five kittens now is pregnant. In another two months, total 6 months, she **and** each of those first five kittens has a litter of 5 kittens, for a total of 25+ 5= 30 new kittens. She now has 20+ 30= 50 "descendants". In another two months, total 8 months, she, each of those first 5 kittens, and her second litter of 5 kittens all have kittens. That is now 5+ 25+ 25= 55 new kittens for a total of 55+ 50= 105 "descendants".

That's the idea. As the months go on, the number of descendants will increase exponentially.