Answer: The required quantity is 7.5.
Step-by-step explanation: We are given to solve the following problem by Rhind Papyrus :
To find a quantity such that when it is added to itself, the result is a 15.
Let x represents the required quantity. Then, the modern day equation that models this problem will be

The solution of equation (i) is as follows :

Thus, the required quantity is 7.5.