Currently, because the CS ratio is 60%, the variable costs must be 40% of sales. If variable costs fall by 10% then they fall by 10% x 40% = 4% and fall to 40 – 4 = 36% of sales.
22.5
The shadow price is the most extra they would be prepared to pay over the normal price. So they would be prepared to pay up to 16 (10 + 6) per kg. They can buy for 14 per kg and therefore they will buy extra (and make extra profit of 16 – 14 = 2 per kg).
The free lectures on both of the these topics will help you.