Consider three concentric circles A, B and C of radii 3, 5 and 10 unit

Answer - B) 525%

Approach - Since this is a question of percentage difference, I understood that there would be a ratio which is why I didn't bother even considering the existence of pi and worked simply on the numbers given, which are very workable numbers.

Area enclosed between circles A and B = 25-9 = 16 sq. units.
Area of circle C = 100 sq. units.
Percentage difference = (100-16)/16, = 84/16 which can be simplified to 21/4, which can be calculated to 525%.

Difficulty Level - Very easy, unless there is something that I missed out on reading, given that this has been marked as 700-level question. It took me about 30 seconds to solve this, most of which was spent calculating 21/4.