The correct option here is "both", as it refers to two or more individuals and indicates that they have been involved together.
Thus, the correct sentence is: "Both employees have been closely associated with the organisation for some time."
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?