You can put this solution on YOUR website! Find the proportion of copper out of the whole mixture:
The percentage of copper as a decimal is 0.768. T give this in the form of a percentage, multiply by 100 and stick a % sign on the end. This will give the percentage of copper is 76.8%
I hope this helps.
P.S. I am trying to start up my own homework help website. I would be extremely grateful if you would e-mail me some feedback on the help you received to adam.chapman@student.manchester.ac.uk