If $$\cos 48^{\circ} = \frac{m}{n}$$ , then $$\sec 48^{\circ} - \cot 42^{\circ}$$ is equal to:

A

$$\frac{m - \sqrt{n^{2} - m^{2}}}{m}$$

B

$$\frac{m - \sqrt{n^{2} - m^{2}}}{n}$$

C

$$\frac{n - \sqrt{n^{2} - m^{2}}}{n}$$

D

$$\frac{n - \sqrt{n^{2} - m^{2}}}{m}$$