120 days in 4 months start day 1 with 4 rats every 4 days 4 rats add on so what I did is this.
Day 1= 4 rats day 4=8 day 8 = 12 so on intell u hit 118 days.but the answer to your question is.. there will be 114 rats if the population of rats double every 4 days for 4 months. hope this is correct and helps. :)