a cyber hacker is trying to identify the mean age of customers that make frequent purchases on the online retail platform. the hacker does not have access to the raw data, however, the hacker had guessed that the age of customers is normally distributed with a standard deviation of 5 years. in addition to the above, the hacker knows that 70% of the time the age of the customers does not exceed 30 years old. calculate the mean age of customers, relying on the above information.