At time=0, investors contributed 100 million to start a bond portfolio.The portfolio manager of bond fund adopted contingent immunization strategy to manage the 100million fund.The manager invested all of their money in the 25-year British Treasury (HM) Bonds with the face value of 100 per unit and a zero coupon rate. With the contingent immunization strategy, hypothetically if the market interest rate goes up by a lot, the portfolio manager has to switch to adopt the classical immunization scheme. Calculate the magnitude of immediate interest rate increase at (t=0) which will let the portfolio manager to immediately switch to the classical immunization strategy given below information-

[1] the market interest rate is 10% p.a. (in semi-annually compounding)

[2] the yield curve is flat

[3] bond fund offers the guaranteed return of 6% p.a. (in semi-annually compounding) to the bond fund contributors

[4] investment horizon of the bond fund is of 10 years