Today is Arif's 12th birthday and his father's 40th birthday. How many years from today will Arif's father be twice as old as Arif at that time?

Arifs age = 12

father's age = 40

let after 'x' years father's age will be twice that of arifs age at that time

therefore

arifs age after x years = 12 + x

father's age after x years = 40 + x

after x years father will twice as old as arif at that time = > (12 + x) * 2 = 40 + x

x = 40 - 24 = 16