4. [-/3 Points] DETAILS SCALCET9 3.7.028. MY NOTES ASK YOUR TEACHER PRACTICE ANOTHER The number of yeast cells in a laboratory culture increases rapidly initially but levels off eventually. The population is modeled by the function a n = f(t) = 1 + be-0.3t where t is measured in hours. At time t = 0 the population is 20 cells and is increasing at a rate of 4 cells/hour. Find the values of a and b. a b