Answer: 600
Explanation:
I did not check your work from parts a and b.
Assuming they are correct,
You have found the total amount after the first year and the total amount after the first two years.
To find the total amount for only the second year,
you subtract the second year totals from the first year totals.
So,
(b) - (a) = 1000 - 400 = 600