<h2>
Hello!</h2>
The answer is: 23.77 hours
<h2>
Why?</h2>

Where:
Total(t) is equal to the amount for a determined time (in hours)
<em>Start</em> is the original amount
<em>t </em>is the time in hours.
For example, it's known from the statement that the bacteria double their population every 15 hours, so it can be written like this:

To calculate how long it takes for the bacteria cells to increase to 300, we should do the following calculation:

So, to know if we are right, let's replace 23.77 h in the equation:
Total(t)=100*2^\frac{23.77}{15}=299.94
and 299.94≅300
Have a nice day!