how to calculate DFt in details

TABLE 9-3 Duration of a Two- Year U.S. Treasury Bond with 8 Percent Coupon and 12 Percent Yield V2 1 112 2 CF 40 40 40 1,040 DF 0.9434 0.8900 0.8396 0.7921 CF, X DF 37.74 35.60 33.58 823.78 930.70 CF, X DF, Xt 18.87 35.60 50.37 1.647.56 1.752.40 1.752.40 DE = 1.883 years 930.70