Gurmanak bought $12,000 of Cenovus Energy (CVE) stock when it was trading for $16.00/share 6 months ago. To finance this position, he borrowed $8000, the maximum he could, from his broker at 6% EAR. He has just sold all his stock for $24/share. What is his annualized rate of return and what can be said of the margin requirement on his account?