Okay. By looking at the question, 2.75 is the distance ran for ½ an hour, because DeAngelo runs at 5.5 miles an hour, but he doesn't run the full 5.5 miles, because of the time. 2.75 is the base. He increases his speed for 1.5 hours for total of 13.25 miles. The equation would be set up as this:
2.75 + 1.5p = 13.25
How to solve it:
We will solve this by subtract 2.75.5 from both sides. 2.75 - 2.75 cancels out. 13.25 - 2.75 is 10.5. We will divide that number by 1.5 now. 1.5p/1.5 cancels out. 10.5/1.5 is 7. There. DeAngelo ran the last 1.5 hours at 7 miles per hour.