Question 718776
First find k in the relationship, {{{A=Pe^(kt)}}}, where t is time in hours, P is initial population, A is population at time t.  The 8 hour case gives you {{{2P=Pe^(k*8)}}}.  Next step, divide both sides by P. Next, take logarithms of both sides.  Maybe this will be enough for you to know how to finish.