Answer: $3850
Explanation:
If the family decides to travel for a day, it will cost them $400 by driving and $550 by flying.
In a week, it will cost them $400 * 7 = $2800 by driving and $550 * 7 = $3850 by flying.
But since the family has not yet decide there mode of transportation, it would be better and advisable they save $3850 in case they decide to fly to their destination and even if they don't, they'll have some money left to spend during there holiday