4. Cleaning is not as enjoyable for Mary as cooking.
5. You ought to see a doctor, I advise.
6. The athletes ought to stretch before and after workouts, as advised by the coach.

4.Mary finds cooking more enjoyable than cleaning.
=> Cleaning is not as enjoyable as cooking for Mary.
5.I advise you to see a doctor
=>You ought  to see a doctor.
6.The coach advises the athletes to stretch before and after workouts.
=> The athletes ought to stretch before and after workouts as advised by the coach.

4.Mary finds cooking more enjoyable than cleaning.
=> Cleaning is not not as enjoyable as cooking for Mary.
5.I advise you to see a doctor
=>You ought to see a doctor.
6.The coach advises the athletes to stretch before and after workouts.
=> The athletes ought to  stretch before and after workouts as advised by the coach.