Computation of Percentage of Copper in the alloy:

Mass % of Copper in alloy = 100 * (Mass of Copper/Total Mass of alloy)

Here,

Mass of Copper = 23 g

Total Mass of alloy = 35g of silver + 4 g of gold + 23 g of copper = 62 g

Mass % of Copper in alloy = 100 * (23 /62) = 37.10%