Let 100 gm of alloy A and 100 gm of alloy B
Gold in alloy A=79×100
copper in alloy A=29×100
Gold in alloy B=718×100
Copper in alloy B=1118×100
Gold in alloy C=7009+70018=210018
Copper in alloy C=2009+110018=150018
Ratio of copper and iron in alloy C=210018:150018
7:5