Answer
a) OPEC would want to try to cut production to increase the price to consumers.
b) OPEC was unable to agree to cut production since the member countries of OPEC each have an incentive to break away from the cartel. (This incentive is more profits from producing more oil.) Since the countries could not agree to a certain oil level, the market doesn't know how much oil will be available for sale. This unknown is what drove the market into turmoil.
Work Step by Step
c) The phrase "do their share" means that OPEC would eventually like to have a relationship with Norway and Britain (since Norway and Britain are producing oil and affecting the world price).