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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def shift(self, delta):
 """Shift this `Series` forward on the X-axis by ``delta`` This modifies the series in-place. Parameters delta : `float`, `~astropy.units.Quantity`, `str` The amount by which to shift (in x-axis units if `float`), give a negative value to shift backwards in time Examples -------- 0.0 m 5.0 m -995.0 m """

        self.x0 = self.x0 + Quantity(delta, self.xunit)