A glass jar contains 6 white, 8 black, 4 red and 3 blue marbles. If a single marble is chosen at random from the jar, what is the probability that it is black or blue?

A

$$\frac{8}{21}$$

B

$$\frac{11}{21}$$

C

$$\frac{5}{21}$$

D

$$\frac{1}{7}$$