In $$\triangle ABC$$, if $$\angle B = 90^\circ, AB = 21$$ cm and $$BC = 20$$ cm, then $$\frac{1 + \sin A - \cos A}{1 + \sin A + \cos A}$$ is equal to:

A

$$-\frac{3}{5}$$

B

$$\frac{2}{5}$$

C

$$-\frac{2}{5}$$

D

$$\frac{3}{5}$$