Let $$\Delta$$ be the area of the region $$\{(x,y) \in \mathbb{R}^2 : x^2 + y^2 \leq 21, y^2 \leq 4x, x \geq 1\}$$. Then $$\frac{1}{2}\left(\Delta - 21\sin^{-1}\frac{2}{\sqrt{7}}\right)$$ is equal to

A

$$2\sqrt{3} - \frac{1}{3}$$

B

$$\sqrt{3} - \frac{2}{3}$$

C

$$2\sqrt{3} - \frac{2}{3}$$

D

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