Aculture started with 4,000 bacteria. after 2 hours it grew to 4400 bacteria. predict how many bacteria will be present after 13 hours round your answer to the nearest whole number.

 idk why they want the dratted "k" . it is so simple w/o it ! 
in the form y = ab^x, a = 4000, b = 4400/4000 = 1.1, x = t/2 
N = 4000*1.1^(13/2) = 7432 < 
 
now you won't be satisfied with simplicity, so 
4400 = 4000e^2k 
e^2k = 1.1 
k = ln 1.1/2 = .0477 to 4 dp 
N(13) = 4000e^(13*.0477) = 7436 < 

note that apart from a roundabout way, you get a less accurate ans !