Math Is Fun Forum

Here is a question from a test I recently I just took. My teacher and I disagree on the answer.

"A printer printed a card with black ink on blue paper and an envelope with blue ink on blue paper. If the colors were chosen at random from a stock of 7 inks and 6 papers, what was the probobility of the given result?"

He thinks it is 1/21. I think it is 1/1764. He says that the reason that it is 1/21 is that there are two seperate events, but he cannot explain this any further, and I am not convinved.

Can anyone help me on this?

Thanks.