A cellular phone tower's signal covers a circular area with a radius r in miles. The strength of the signal is increased, and now covers an area of \pi r^{2}+6\pi r+9\pi square miles. By how much did the radius of the coverage increase?
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Question 6
6.
Arthur is putting a wall aroud his square castle. The area of the castle is 10000 square feet. The sides of the wall are 70a. Write an expression, using the difference of squares, to represent the area between the walls and the castle.