The correct answer is: By reference to the custom of a particular trade or locality where the contract is silent on the point.

In the absence of an express term the courts will imply a term if customary practice can be applied.

Terms will be implied by the courts to give a contract business efficacy if the parties intended those terms to apply but they were not mentioned because they were taken for granted or were inadvertently omitted. They will not imply terms contrary to express terms.

The courts will not attempt to make a contract reasonable. They will merely imply terms to give it efficacy.

Terms are not implied through course of dealings where there is an express term to the contrary.