If I give my brother 2 marbles I will have double his number of marbles, but my friend will have triple the number I do. The total number of marbles we have together is 63. How many marbles do I have?
Step-by-step reasoning:
16
Let X be the number of marbles I have.

If I give my brother 2 marbles, I'll have X - 2 marbles left.

And my brother will have (X - 2) / 2 marbles.

And my friend will have (X - 2) * 3 left.

So the total number of marbles is X - 2 + (X - 2) / 2 + (X - 2) * 3 = 63.

(X - 2) * 9 / 2 = 63.

X - 2 = 14.

X = 16 marbles.

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The answer is 16