At least a third of Fred's marbles are dark blue. All of the rest are red, except for 4 that are green. If he has 63 marbles, how many of them are red?
Please answer and provide answer explanation.
38
Fred has 63 / 3 = 21 dark blue marbles.

Fred has 63 - 21 = 42 red and green marbles.

Fred has 42 - 4 = 38 red marbles.

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The answer is 38