What is the value of $$[(\sin 7x - \sin 5x) \div (\cos 7x + \cos 5x)] - [(\cos 6x - \cos 4x) \div (\sin 6x + \sin 4x)]$$?

A

1

B

$$2 \tan x$$

C

$$\tan 2 x$$

D

$$\tan (\frac{3x}{2})$$