The number of bacteria in a certain population increases according to a continuous exponential growth model, with a growth rate parameter of 9.8% per hour. how many hours does it take for the size of the sample to double? do not round any intermediate computations, and round to the nearest hundredth.

Bacteria population increases by 9.8% per hour.
Population = (1.098)^hours
Solving this for time we get:

Time = log(ending amount / beginning amount) ÷ log (1 + rate)


Since we must solve the problem for the population to double, we'll say 
beginning amount = 100 and ending amount = 200
Time = log(200 / 100) ÷ log (1 + .098)

Time = log(2) ÷ log (1.098)
Time = 0.30102999566 / 0.040602340114
Time = 7.4141045766 Hours

Time = 7.41 Hours (rounded to nearest hundredth.

Source:
http://www.1728.org/expgrwth.htm

The answer maybbe c