suppose x grams copper.. then 36-x grams gold.

now the upthrust was 2 grams. (36 -34)

so we say v d g = 2 x 10   (taking g = 10)

or v d = 2

the volume occupied by x grams copper = x / 8.9 and volume occupied by gold = 36-x / 19.3

the net volume of water displaced = x / 8.9 + 36-x / 19.3

d = 1 for water.

so x / 8.9 + 36-x / 19.3 = 2