Example 4 The bid-ask spread on XYZ stock is always 0.30. Laura decides to short-sell 100 shares of XYZ on January 1 st when the ask price is 30 . Laura's broker charges 20 per trade. XYZ pays dividends of 0.15 per share at the end of every quarter. Ignore any interest on dividends. Laura must deposit 40% of the net proceeds received from the sale of stock as collateral. The market rate of interest is 6% effective per year, but the short rebate is only 5% effective per year. Laura will close her position on December 31st after the dividend is paid. What range of ask prices on December 31st will result in a positive profit for Laura? Assume unearned interest on the collateral at market rate is a loss