Answer: The cause-and-effect relationship in "The Bridge" that relates to the theme "Sometimes help is found in the most unexpected of places" is Because the narrator’s math tutor explains the mathematical benefits of music to the narrator’s parents, the narrator is able to rejoin his band.
Explanation: A cause-and-effect relationship consists in indicating what were the reasons behind an event or situation as well as what were the consequences of this event/situation. The sentence "Because the narrator’s math tutor explains the mathematical benefits of music to the narrator’s parents, the narrator is able to rejoin his band" presents the cause in the first clause ("Because the narrator's math tutor explains the mathematical benefits of music to the narrator’s parents") and the effect in the second clause ("the narrator is able to rejoin his band"). Moreover, this sentence is related to the theme "Sometimes help is found in the most unexpected of places" because the narrator's math tutor is the one that finally convinces the narrator's parents about the benefits of doing music. Therefore, the narrator received help from someone he would have never expected: his math tutor.