In the case of our 'string around the Earth' puzzle, the radius is being increased by 15cm, so we need to know that as a fraction of the original radius. So what is the radius to start with?

NPR's Ayesha Rascoe plays the puzzle with WBAA listener Bob Kozak of Lafayette, Indiana, and Weekend Edition Puzzlemaster Will Shortz. In honor of Earth Day on Tuesday, I've brought a game of ...