6. Circle A has a radius of 10 units and Circle B has a radius of 5 units. The center of Circle B is on the circumference of Circle A. What is the difference between the area which is within A but not B and the area which is within B but not A. Put your answer as a multiple of Pi.
30. Marna baked a batch of brownies in a 9x12 pan. She then decided to created a giant ice cream sandwich by cutting two congruent circular brownies out of the pan and placing a wedge of chocolate chip ice cream between them. What is the radius of the largest circular brownies she can cut? Express you answer as a common fraction in simplest radical form