You know that:
- Last weekend his trip took 10 hours when he drove to the mountains.
- When he drove home, the trip took 7 hours.
- His average rate was 18 miles per hour faster on the trip home.
By definition, the distance can be calculated with this formula:
![d=rt](https://img.qammunity.org/2023/formulas/physics/college/z3wm8hcqqd9gaomwja5ax7i09qs7omsisg.png)
Where "d" is distance, "r" is rate, and "t" is time.
Then, you can set up the following equation to represent his trip to the mountains ("d" is in miles):
![d=10r](https://img.qammunity.org/2023/formulas/mathematics/high-school/atne4uo7sm14pc2xjo3tu68qpnv152h5b5.png)
And you can set up the following equation to represent his trip home ("d" is in miles):
![d=7(r+18)](https://img.qammunity.org/2023/formulas/mathematics/high-school/3bd5apzk9w5ukbwm0qwuzox6l2kt4gii0o.png)
To find the value of "r", you need to make both equations equal to each other and solve for "r". Then, you get:
![\begin{gathered} 10r=7(r+18) \\ 10r=7r+126 \\ 10r-7r=126 \\ \\ r=(126)/(3) \\ \\ r=42 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/7m030xhp1h8wjslvwxqal74hx5wus0apm8.png)
Knowing the value of "r", you can substitute it into the second equation:
![\begin{gathered} d=7\mleft(r+18\mright) \\ d=(7)\mleft(42+18\mright) \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/bgewztxgxuhbmk9xzn0orgwqd6lxqbylbg.png)
Finally, evaluating, you get (Remember that "d" is in miles)
![\begin{gathered} d=(7)(60) \\ d=420 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/high-school/4krr8ib03lbrkfdac0r0uul8u0d2nm713p.png)
Therefore, the answer is:
![420\text{ }miles](https://img.qammunity.org/2023/formulas/mathematics/high-school/n5rwg68av2pzl60d5dv80pvcezf4vhyvcn.png)