On Jan 1, you sold short 400 shares of Microsoft at $50 per share. You post $10000 to the margin account. On April 1, you received a margin call on this trade. Assume the minimum margin requirement is 25% and you receive a margin call.

What amount must you top-up to restore to a 50% margin?

A)$3000

B)$4000

C)$5000

D)$6000

E)None of the above