Algebra-1

1. Determine the number of doubling periods:

Since the number of plants doubles every 3 days and we want to know the number of plants after 9 days, we divide the total number of days (9) by the length of each doubling period (3). So the number of doubling periods  is .

2. Use the exponential growth formula:

The formula for exponential growth in this case is , where:

 is the final number of plants.

 is the initial number of plants. Here,  (because we started with 4 seeds that grew into plants).