A group of laboratory animals is infected with a particular form of bacteria. Their survival time is found to be normally distributed , with a mean of 28 days and a standard deviation of 12 days. a). What percentage of these animals will survive for less than 16 days? b). Given the probability that one of these animals survives for less than 36 days is 0.7486 (to 4 decimal places), find the portability that one of these animals survives for between 20 and 36 days?