6 Every marble in a jar has either a dot, a stripe, or both. The ratio of striped marbles to non-striped marbles is 3:1, and the ratio of dotted marbles to non-dotted marbles is 2:3. If six marbles have both a dot and a stripe, how many marbles are there all together? (A) 16
(B) 18
(C) 20
(D) 40