Option 4 : Rs. 2550

**Given,**

Ratio of number of boy's gift to girl's gift = 60 : 85 = 12 : 17

Let the price of a boy's gift and the price of a girl's gift be Rs. A and Rs. B respectively.

Then,

⇒ A + B = 320

⇒ A – B = 20

Solving,

⇒ A = 170

⇒ B = 150

Ratio of price of boy's gift to the price of girl's gift = 170 : 150 = 17 : 15

Using compound ratio,

Ratio of total price of boys gift to the total price of girls gift =

= (12 : 17) and (17 : 15)

= 4 : 5

Total price of all 145 gifts = 60 × 170 + 85 × 150 = Rs. 22950

Given,

Difference in their contribution = 22950 × 5/9 – 22950 × 4/9 = Rs. 2550