x2 = [10.5, -6.36, 11.56, 19.06, -4.37, 26.56, 9.38, -33.12, -8.44, 0.31, 
    -13.44, -6.25, -13.44, -0.94, -0.94, 19.06, 0.31, -5.94, -13.75, -23.44,
    -51.68, 10.5]
x3 = []
Python -subtraction of value within a list