Answer:
1800 oz.
Explanation:
There are already 600 ounces of alloy of nickel.
Of this 600 oz, 50% is pure i.e. copper content = 600(0.5) = 300 oz
Now available is
Copper Other metals
300 300
Let x oz of 10% copper is added.
Then new alloy will have 300+0.1x oz copper in total of 600+x oz.
Percentage pure =

Simplify to get

Hence answer is 1800 oz should be added.