If $$a^4 + b^4 + a^2b^2 = 273$$ and $$a^2 + b^2 - ab = 21$$, then one of the values of $$\left(\frac{1}{a} + \frac{1}{b}\right)$$ is:

A

$$-\frac{9}{4}$$

B

$$-\frac{3}{4}$$

C

$$\frac{9}{8}$$

D

$$\frac{3}{2}$$