Which situation is best modeled by an exponential function? the amount of a substance remaining after x years if it is decreasing at a rate of 25% annually the number of gas stations in a town that had 4 stations in 2010 and x new stations have opened each year since the distance a car is from a fixed point if the car was originally 200 feet from that point and traveled at a speed of x miles per hour the cost to rent a bicycle from a company that charges a flat rate plus x dollars per day