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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 est_gaba_conc(self):
 """ Estimate gaba concentration based on equation adapted from Sanacora 1999, p1045 Ref: Sanacora, G., Mason, G. F., Rothman, D. L., Behar, K. L., Hyder, $\gamma$-aminobutyric acid levels in depressed patients determined by proton magnetic resonance spectroscopy. Archives of general psychiatry, 56(11), 1043. """

        # need gaba_auc and creatine_auc
        if not hasattr(self, 'gaba_params'):
            self.fit_gaba()

        # estimate [GABA] according to equation9
        gaba_conc_est = self.gaba_auc / self.creatine_auc * 1.5 * 9.0
        
        self.gaba_conc_est = gaba_conc_est