At the end of day 0, you go short in 10 futures contracts; each contract is for a single unit of an underlying commodity with a futures settlement price at the end of day 0 of $252. This is the futures price for you at the end of day 0, therefore there is no marking to the market for you on that day. The initial margin is $12 per contract and the maintenance margin is $10. Over the following three trading days, this futures has end-of-day settlement prices of $251 at t=1, $255 at t=2, $251 at t=3. If there is a margin call during the three days, what is the variation margin and on which day do you have to pay it?