If $$\left( {x - \frac{1}{x}} \right){\text{ = }}\sqrt {21} {\text{,}}$$then the value of $$\left( {{x^2} + \frac{1}{{{x^2}}}} \right)$$ $$\left( {x + \frac{1}{x}} \right)$$is = ?

• A. 2
• B. 3
• C. 15
• D. 20
• E. 25