Yak Travel Agency arranges trips for climbing Mount Everest. For each trip, they charge an initial fee in addition to $0.15 for each vertical meter climbed. For instance, the price for climbing all the way to the summit, which is 3500 meters above the base of the mountain, is $645. Let y represent the fee (in dollars) of a trip where they climbed x vertical meters.

the equation for the relationship between the fee and vertical distance.

y=