The concentration of E. coli bacteria in a swimming area is monitored after a storm:

The time is measured in hours following the end of the storm and the unit CFU is a "colony forming unit" Use this data to estimate.
(a) The concentration at the end of the storm (t = 0) and
(b) The time at which the concentration will reach 200 CFU/100mL. Note that your choice of model should be consistent with the fact that negative concentrations are impossible and that the bacteria concentration always decreases withtime.
 

t (hrs) 4 8 12 16 20 24 e (CFU100 nL) 1590 1320 1000 900 650 560