Hi kjames,

Sorry, but I'm tied up doing something else for quite a while, and so I can only give a quick answer that isn't exact (it's a decimal approximation), and as I got it with Excel's Goal Seek I can't give the method you probably want, either.

Here's what I got:

Copper: add 33.846153846154 lbs

Magnesium: add 73.846153846154 lbs