If $$a \ast b = \frac{a + b}{a - b}$$, then the value of $$\frac{13 \ast 6}{5 \ast 2}$$ is

A

$$\frac{21}{4}$$

B

$$\frac{17}{3}$$

C

$$\frac{19}{39}$$

D

$$\frac{57}{49}$$