32, 38, so on. So its +4 then +8 then +12 +16 +20....
Subtract that number down so its a
Month goes on the x axis and the length goes on the y axis.
You're starting at 400. Each time you're cutting in half.
So the common ratio is 1/2 which means the equation is

which is in the geometric sequence format. So the answer is choice D