First Principles Thinking: Futures Margin Mechanics
A is correct.
Price change:
$$ 1{,}770 - 1{,}800 = -30 $$
Total loss:
$$ 30 \times 100 \times 10 = \text{USD } 30{,}000 $$
Initial margin balance is \( \text{USD } 100{,}000 \). After the loss, the balance is \( \text{USD } 70{,}000 \). Maintenance margin is \( 7{,}500 \times 10 = \text{USD } 75{,}000 \), so a margin call is triggered. The account must be restored to the initial margin level, so the required deposit is:
$$ 100{,}000 - 70{,}000 = \text{USD } 30{,}000 $$
B is incorrect because it only restores the account to maintenance margin.
C is incorrect because it does not restore the account to initial margin.