Solution to the Problem:
The answer is: Jill would take 6.3 minutes or 6 minutes 18 seconds to run the 1/2 mile.
Let x = Jill's rate going up the hill. Then her rate down the hill would be 1.5x.
Let y = Jack's rate going up the hill. Then his rate down the hill would be 1.5y.
Equate Jill's time when she meets Jack with Jack's time when he meets Jill.
Then equate Jill's total time plus 1/2 minute with Jack's total time.