6. The number of yeast cells in a laboratory culture increases rapidly initially but levels off even- tually. The population is modeled by the function n = f(t) = 1 + be 0.71 ' where t is measured in hours. At time * = 0 the population is 20 cells and is increasing at a rate of 12 cells/hour. Find the values of a and b. According to this model, what happens to the yeast population in the long run