This is a geometric progression problem. We can the general formula that can tell us how many flowers would be planted each month.
Let's write the terms that we know and see if we can find the pattern:

The patern here is obvious. Let's write it down:

This formula gives us a number of flowers planted in the n-th month.
Answer:
I think the last you already have is right. I wasn’t very good at this but I try
Step-by-step explanation:
Two sides are the same length one angle measures 90 degrees
2x squared would be you final answer