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Answer:
8 hours
Steps:
Train 1:
Hours: 1, 2, 3, 4, 5, 6, 7, 8
Miles: 75, 150, 225, 300, 375, 450, 525, 600
Train 2:
Hours: 1, 2, 3, 4, 5, 6, 7, 8
Miles: 0, 0, 100, 200, 300, 400, 500, 600
Every time the y-value decreases by 1, the x-value increases by 2, so the slope is -1/2 throughout the line.
The length of the line is 21.