Step 2 of 3 : The slope is equal to the rate that the IV solution is the dispensed per hour. What is the slope? (Hint: consider whether the amount of IV solution in the bag is increasing or decreasing and how this would affect the slope.)

The slope is the slope at which the solution is dispensed per hour, and since the amount of solution in the bag is decreasing, it has a negative sign.
It means that the slope is -100.