You have the following formula given in the exercise:

Where "r" is the annual growth rate (expressed as a decimal) and "t" is the time in years.
Based on the information given in the exercise, you know that the annual growth rate is 6%.

Notice that 6% can be expressed as a decimal number by dividing it by 100.
Since the information provided is from 1900 to 1950, you can identify that:

Now you can substitute values into the formula and evaluate:

Therefore, the answer is: Option a.