def calc_ch4_mr(sample, quantifier, standard):
    """
    Calculate mixing ratio of a sample when provided with the sample to quantify it against, and the Standard that was
    run in the quantifier.

    :param sample: Sample, a valid sample (use valid_sample(Sample) to verify)
    :param quantifier: Sample, a valid sample ("") that will be used to quantify the provided sample
    :param standard: Standard, the standard that was run.
    :return: Sample, the same object but returned with it's peak given a mixing ratio
    """
    sample.quantifier = quantifier
    sample.peak.mr = (sample.peak.pa / sample.quantifier.peak.pa) * standard.mr
    sample.standard = standard

    return sample