Which one is smaller 2/7 or 1/21

52 cm radius = diameter = area = circumference = circumfer

Ineed the solution to this problem and the steps.

Problem number 26 of the rhind papyrus says: find a quantity such that when it is added to of itself the result is a 15. the modern day equation that models this problem is x + x = 15. what is the solution to the equation? x = 10 x = 12 x = 15 x = 30