Answer:
Question is incomplete so I'll use a reference.
Assume the person whose house the car went to is 21 miles away.
The car would have had to go back and forth so the total distance spent would be:
= 21 + 21
= 42 miles
The car uses 1 kilowatt hour to go 3 miles. Now it has to go 42 miles.
The number of kilowatt hours it will need are:
= Distance / distance per kilowatt hour
= 42 / 3
= 14 kilowatt hours
