If tan θ =\(\frac{20}{21}\), then the value of \(\frac{{\sin \theta - \cos \theta }}{{\sin \theta + \cos \theta }}\) is:

• A. \(\frac{-1}{41}\)
• B. \(\frac{29}{35}\)
• C. \(\frac{27}{21}\)
• D. \(\frac{-29}{31}\)