The general Formula for a decreasing Annuity is:

For this example we have:
P = 78,000
n = 7*4 = 28
i = 8%/4 = 2% = 0.02
After substituting you can find value for R, rent.
None, you wrote a different function than the one in the picture.
The answer to the picture is the last graph
Answer:
A
Step-by-step explanation:
The average is over the months not added each month