Harrison makes $$30$ an hour as a plumber. He must take two hours off work to have a tooth extracted. His contract does not cover these events. The dentist charges $$80.$ The opportunity cost to the firm of Harrison's trip to the dentist is

Select one:

a$.$ $$140.$

b$.$ $$60.$

C$.$ $$80.$

d$.$ $$0.$

e$.$ $$110.$