Answer:
impossible
Explanation:
If the customers choose to rebook a holiday that is more expensive than the original holiday in Portugal, and the holiday company is offering an incentive worth up to 20% of the value of the holiday, the customers will have to pay the difference between the original holiday and the new holiday, minus the 20% incentive.
Without more information on the cost of the new holiday, it is impossible to determine how much extra it will cost the customers each