For this case, the first thing we must do is define a variable.
We have then:
p: rate in miles per hour for the last 1.5 hours
We now write the equation that models the problem.
We have then:
![(0.5) * (5.5) + 1.5p = 13.25](https://img.qammunity.org/2019/formulas/mathematics/middle-school/hqfgx8sbivllmn2utd6p09k1d6d5k6osux.png)
Rewriting we have:
![2.75 + 1.5p = 13.25](https://img.qammunity.org/2019/formulas/mathematics/middle-school/pg742mxlnh24ayryjapqnewwbj531dfguf.png)
From here, we clear the value of p.
We have then:
Answer:
DeAngelo's rate for the last 1.5 hours of his run is 7 miles per hour.