def project_beta(tax_rate, asset_beta, debt_to_equity):
    """
    Summary: Calculate the project beta for subject firm.
    
    PARA tax_rate: Company's marginal tax-rate.
    PARA type: float
    
    PARA asset_beta: A comparable publicly traded company's asset beta.
    PARA type: float
    
    PARA debt_to_equity: Company's debt-to-equity ratio.
    PARA type: float
        
    """     
    
    return asset_beta * (1 + ((1 - tax_rate)*debt_to_equity))