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I'm having some trouble with my algebra homework. Please walk me through the question completely and give me the answer so I can fully understand it if I would ever need to solve a similar problem.

Here's the problem:
#1: Jon begins jogging at a steady 3 meters/sec down the middle of Lane #1 of a public track. Laura starts even with him in the center of Lane #2 but moves at 4 meters/sec. At the instant they begin, Ellis is located 100 meters down the track in Lane #4, and is heading towards them in his lane at 6 meters/sec. After how many seconds will the runners lie in a straight line?

a. Let t be the number of seconds the three have been running. Write expressions for the number of meters each has run after t seconds.

b. Consider the location of each runner as a point on a graph. What quantity might you use as the x-coordinate? What quantity might you use as the y-coordinate?

c. How can you tell if three points are on a line? Use this to solve the problem.

Thanks so much in advance. Any help is appreciated, even if you can only solve one part. Thanks!