A bacteria culture starts with 640 bacteria and grows at a rate proportional to its size. After 2 hours there will be 1280 bacteria. (a) Express the population P after t hours as a function of t. Be sure to keep at least 4 significant figures on the growth rate. P(t)= (b) What will be the population after 5 hours? bacteria (c) How long will it take for the population to reach 1670? Give your answer accurate to at least 2 decimal places. hours