**Rs. 30**

Given- Rs. 200

Exchange- 0.5x+2y+10z<200

Ratio- x/y/z=18/13/9

Cost of 2x chocolates=?

With minimum coefficient of 1, the amount will make 18*0.5+13*2+9*10=125 Rs., if doubled it will be greater than Rs. 200 so the exchange was Rs. 125.

5x chocolates cost Rs. 200- Rs. 125= Rs. 75, so 2x chocolates cost Rs. 2*75/5= **Rs. 30**