A dental insurance policy covers three procedures; orthodontics, fillings and extractions. During the life of the policy, the probability that the policyholder needs

- Orthodontics work is 1/2

- Orthodontics work or filling 2/3

- Orthodontics work or an extraction is 3/4

- A filling and an extraction is 1/8

The need for orthodontic work is independent of the need for a filling and is independent of the need for an extraction.

Calculate the probability that the policyholder will need neither a filling nor an extraction during the life of the policy.