A company's profit is modeled by the equation $P = 50s - 800$, where $s$ is the number of units sold. What does the rate of change, 50, represent?

The starting profit is 50 dollars.

The company sells 50 units per day.

The profit increases by 50 dollars for each unit sold.

The company has fixed costs of 50 dollars.

Which of the following scenarios describes a relationship with a positive rate of change?

The remaining pages in a book you are reading.

The amount of fuel in a car during a long trip.

The height of a burning candle.

The total distance walked by someone at a constant pace.