The number of yeast cells in a laboratory culture increases rapidly initially but levels off eventually. the population is modeled by the function n=f(t)=a/1+be^-0.7t where t is measured in hours. at time t = 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?