Given information is not enough to answer your question appropriately. Let me start explaining with the cases that we can extract from given information:
Case 1: Stacy was driving the car - in this case, Stacy was in driver seat.
Case 2: Someone else was driving the car - in this case, Stacy was in passenger seat.
Answer:
It proves that the boys aren't taking Ralph's move seriously. It reveals how angry the boys are that Ralph is moving away.
Explanation:
The gerund in the sentence provided above is backpacking. Gerunds are verbs in -ing form but function as a noun. In this sentence, it functions as a direct object because it answers the question "what". By this, we can construct the question "What popular pastime is being talked about?".
