ANSWER

Step-by-step explanation
Let her average rate on the trip to the mountains be x miles per hour.
This implies that her average rate on her way home was (x + 18) miles per hour.
The distance traveled can be found using the formula for speed(average rate):

Therefore, on her way to the mountains:

And on her way home:

Since the distance is the same for both trips, equate the two equations:

Solve for x in the equation:

Substitute the value of x into the equation for distance to find the distance:

That is the distance from the mountains to where Tammy lives.