Due to your renown as a Mathematician, Gandalf has hired you as a part-time member of the Fellowship of the Ring, who have been tasked with destroying the One Ring. Gandalf knows that Sauron's power can be modeled with the equation P(x) = -x2 - 50x + 10,000 where x is the distance (in miles) between the One Ring and Mt. Doom. The Fellowship is traveling towards Mt. Doom at a rate of 30 miles per day (that is, the rate of change of distance is -30 miles per day). Find out the (time) rate of increase in Sauron's power when the Fellowship is 75 miles from Mt. Doom.