It has been claimed that the "productivity level" of people in different fields can be described as a function of their "career age" t by p(t)=eat-ebt where a and bare constants which depend on the field of work, and career age is 20 less than the actual age of an individual. The constants for mathematicians, geologists, and historians are estimated in the table below. Field a b mathematician 0.03 0.05 geologist 0.02 0.04 historian 0.02 0.03 What is the career age when an individual in each field reaches maximum productivity level