Question

PLEASE HELP ME!

Answer 1

You want to know how long it'll take for the bacteria to grow
to (800/500) = 1.6 times their initial population.

The number of double-times it'll take is 

                         [ log(1.6) / (log(2) ]  =  0.6781 .

The double-time for these particular critters is 12 hours,
so it'll take them

                             0.6781  x  12 hours  =  8.137 hours

                                                                =  8 hours  8.2 minutes .