Need help with these 2 questions please I been struggling all day

At the beginning of 1990, 20.8 million people lived in the metropolitan area of a particular city, and the population was growing exponentially. The 1998 population was 23 million. If this trend continues, how large will the population be in the year 2011? The population will be million people. (Round to the nearest integer as needed.)The half-life of plutonium-241 is approximately 13 years. a. How much of a sample weighing 2 g will remain after 90 years? b. How much time is necessary for a sample weighing 2 g to decay to 0.1 g? a. After 90 years, g will remain. (Do not round until the final answer. Then round to four decimal places as needed.)