A travel agent studies examples of one-way airfares between cities across the United States. To predict any airfare, she proposes the formula A = 150 + 0.2x, in which A is the airfare in dollars and x is the distance of the flight in miles. Based on the formula, what is the difference in airfare between a flight of k miles and a flight of k + 1 miles?
What does the graph of the equation A = 150 + 0.2x represents ?