Final answer:
The idiom 'watch the musical play for free' has the context clue 'my uncle... is buying us two tickets,' which acts as a synonym, indicating that the students will not have to pay for the tickets.
Step-by-step explanation:
The student is asked to find a context clue for the meaning of an italicized idiom and determine whether this clue is a synonym or an antonym. In the sentence given, "My uncle who mans the ticket booth is buying us two tickets," indicates that the uncle is providing the tickets at no cost, which is a synonym for "watch the musical play for free." Thus "buying us two tickets" serves as a synonym (SYN) rather than an antonym (ANT) because it is an alternative way to express that they will get to see the play without payment, rather than the opposite.