Tristan rode his scooter from his home to his school. the following graph represents his trip, relating the time, x, to the distance, y.

1.  Tristan road a total distance of 7 miles.

2. The part of the graph that is a horizontal line shows that Tristan traveled 0 miles for 15 minutes.

3. The slope of this graph can not be negative because total distance is not a negative number.  Distance is a number that increases over time.

Step-by-step explanation:

Given the graph of Tristan's scooter trip from home to school, you can see that it is increasing for the first 10 minutes, constant for 15 minutes and increasing for another 10 minutes.  This would indicate that he was moving at a steady pace the first three miles, then stopped to take a break/talk to friends for 15 minutes, and then rode the remaining 4 miles to school.  Looking at the graph of miles versus minutes, you can see that after 35 minutes, he traveled a total of 7 miles and his break at mile 3 was from 10 - 25 minutes, or 15 minutes total.  Distance is always a positive number, as it is not possible to travel negative miles.