Can you explain why rent no need to count in the MMR formula?

Lehman Brothers 50% 30% $65 1,000 Shares Initial Margin Maintenance Margin Initial Price Sale Proceeds $65,000 Margin $32,500 Stock Owed 1,000 shares Price drops to $0 at year end Rent $1 per share How much can the stock price rise before a margin call? (Initial margin + sale proceeds market value)/market value = MMR ($65,000 + $32,500 - 1,000P) / (1,000P) = 30% P = $75.00