Correct Answer - Option 2 : 36 gm

**Given:**

Ratio of Zinc and Copper = 7 : 5

Ratio of Zinc and Copper after adding Zinc = 6 : 3

**Calculation:**

Let Zinc = 7x and Copper = 5x

According to question:

7x + 5x = 12x

12x = 144

X = 144/12 = 12

Zinc = 7x = 7 × 12 = 84gm

Copper = 5x = 5 × 12 = 60gm

Let Y gm Zinc should be added to make the ratio 6 : 3

⇒ {(84 + Y)/60} = 6/3

⇒ 252 + 3Y = 360

⇒ 3Y = 360 – 252

⇒ 3Y = 108

⇒ Y = 108 / 3 = 36

**∴ 36gm Zinc should be added to make the ratio 6 : 3.**