Answer: So when you double the radius, the area goes up by 4 times because 2 squared is 4. The area will always go up by the square of how much the radius goes up. By contrast, the circumference will only double -- from 12.56 to 25.12 because you do not square the radius (or diameter) -- you just multiply it by pi.
12x minus -3x is the same as adding two positives. That gives us 15x. 4 - 5 is -1. Putting the two simplified parts of the expression together, we get 15x - 1. Mason is correct.
