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