The number of persons infected by a particular virus for the first 30 days was equal to the square of the number of days. After 30 days, the number of infected persons doubled every 4 days. At the end of 50 days, 3,800 persons had died and on subtracting their number from the total number of cases, the number of infected persons was found to double every 5 days. After how many days of the onset of the infection, did the number of infected persons become 4 lakh?