Can someone show me the formula and the way to solve this please.

A newly issued U.S. Federal T-Note matures in exactly 7 years. The coupon rate is 4% per year and coupons are paid semiannually. The bond is priced at 103.64 (per $100 offace value) and yields 3.41%. The economy is slowing and many forecasters predict a recession. You expect that the monetary authorities will relax monetary policy which will cause interest rates to fall. You expect the yield on the 7-year bond to fall to 2.16%. The bond has a face value of $1 M. if you want to earn $1 M by investing in bonds to prot from the interest rate change, how many bands do you buy? In order to earn $1 M by investing in bonds, you need to buy bonds. (Round up to the nearest whole number.)