Answer:
 d.  None of the above
Step-by-step explanation:
We assume the sequence of deposits is ...
 month 0: $400
 month 1: $200
 month 2: $200
...
 month 240: $200 . . . . accumulated interest is determined at this point
That is, no interest is earned on the last deposit.
_____
The value of the initial $400 deposit after 20 years at 2.15% interest compounded monthly is ...
 $400×(1 +.0215/12)^(12×20) = $400×1.536666 ≈ $614.67
The value of the $200 annuity at the same interest rate is ...
 $200((1 +.0215/12)^(12×20) -1)/(.0215/12) = $200×299.534612 ≈ $59,906.92
So, the total account value is ...
 $614.67 +59,906.92 = $60521.59
The total amount deposited was ...
 $400 +$200×240 = $48,400
The interest earned is the difference between the account value and the total of deposits:
 $60,521.59 -48,400 = $12,121.59 . . . . interest earned
This value does not match any numerical answer choice, so we conclude the appropriate answer is ...
  None of the above
