<image>During the "Golden Week" holiday, the change in the number of people traveling in a certain city over 7 days is shown in the table below (positive numbers indicate an increase compared to the previous day, and negative numbers indicate a decrease compared to the previous day).

(1) Assume the number of people traveling on September 30 is a. Express the number of people traveling on October 2 as an algebraic expression in terms of a;
(2) Determine which day within the seven days had the highest number of people traveling and which day had the lowest number of people traveling. What is the difference in the number of travelers between these two days? If the day with the highest number of travelers saw 30,000 people traveling, how many people traveled on September 30?