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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 write_u2d(self, u2d):
 """ write a flopy.utils.Util2D instance to an ASCII text file using the Util2D filename Parameters u2d : flopy.utils.Util2D Returns ------- filename : str the name of the file written (without path) """

        filename = os.path.split(u2d.filename)[-1]
        np.savetxt(os.path.join(self.m.model_ws,self.arr_org,filename),
                   u2d.array,fmt="%15.6E")
        return filename