Answer:

Explanation:
Let y represent the total fee (in dollars) of a trip where they climbed x vertical meters.
We know that there is an initial fee of $100, so we know that if we climb x=0 meters, we have a fee of y(0)=100.

As there is a constant fee (lets called it m) for each vertical meter climbed, we have a linear relationship as:

We know that for x=3000, we have a fee of $400, so if we replace this in the linear equation, we have:

Then, we have the equation for the total fee in function of the vertical distance:
