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The mass of a 6-C-12 atom is 19.92679*10^-24 g and that of a 2-He-4 atom is 6.64658*10^-24 g. If the international atomic weight scale had defined the mass of a 2-He-4 atom as exactly 4.0, what would be the atomic weight of Li which is a 6.941 on the present scale?

A long time ago, I had 6.936 as an answer, which was right. But now that I go back to it, I keep getting 6.946 and I don't see why I got 6.936 before. I've tried doing (6.64658*10^-24/12)/(19.92679*10^-24/4)*6.941=6.946. Can someone please tell me what I'm doing wrong?