是不清楚的,which 可以修饰 an equal part 也可以是 cost of the dinner.一般来说会会意为 cost of the dinner,因为是最接近.如果对方是 native speaker 而他想表达的是每人给了 $96,那他应该会这样说:
each of the friends paid $96 to split/share the cost of the dinner