Hi:) is there a reason why the gradient of vertical lines are undefined?

Atrain leaves little? rock, arkansas, and travels north at 90 kilometers per hour. another train leaves at the same time and travels south at 80 kilometers per hour. how long will it take before they are 680 kilometers? apart?

Suppose you are analyzing the relationship between time and distance given in a table,and there are 4 values for each quantity.you divide distance 2 minus distance 1 by time 2 minus time 1.you then divide distance 4 minus distance 3 by time 4 minus time 3 and get a different answer.what can you say about the relationship?

What are the cordinates for point a?