i can't get my formula can some help

80 75.8 76.7 83.3 80.0 0.0
75 70.8 71.8 78.3 73.7 -0.5
70 65.9 66.8 73.2 68.6 -0.6
60 56.1 56.9 63.1 57.6 -1.0