The dependent clauses are "while patrick set the table" (in sentence 1), "if he is running late" (in sentence 2), and "before she boarded the plane" (in sentence 3).
A dependent clause is a group of words that cannot stand on its own as a complete sentence. Dependent clauses can be divided into adjectival, adverbial and nominal clauses. In the case of the sentences provided, the three of them contain adverbial clauses, which means that the dependent clauses are acting as adverbs. Moreover, these clauses have been introduced by the subordinating conjunctions "while", "if" and "before" respectively.
