Question 711106
 person            age
  Jeff              10
  Jeff Brother       2

In P years Jeffs age should be twice as that of His brother
then, Jeff will have (10+P) and His brother (2+P)
but we Say in P years to come, he will have 2(2+P)=10+P
open the brackets to have P=6.

Therefore, after 6 years Jeff's age will be twice as that of his Brother.