U.S. Dollar/British Pound. Assuming the same initial values for the dollar/pound cross rate in the FX Option Pricing workbook, how much more would a call option on pounds be if the maturity was doubled from 90 to 180 days? What percentage increase is this for twice the length of maturity?

An Excel workbook entitled FX Option Pricing is downloadable from this book’s Web site. The workbook has five spreadsheets constructed for pricing currency options for the following five currency pairs (dollar/euro shown here):
U.S. dollar/euro, U.S. dollar/Japanese yen, euro/Japanese yen, U.S. dollar/British pound, and euro/British pound. Use the appropriate spreadsheet from the workbook to answer this problem.