Question 518308
Man's age = 40
Sons's age = 14

Let 
Number of years =  x  
father will be = 40 + x
Son will be = 14 + x

Twice the age of son after x years =  father's age after x years
2(14+x)=40+x
28+2x=40+x
2x-x=40-28
x=12


After 12 years father will be twice as old as his son.

Check
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Man's age = 40 +12 = 52 (which is twice of 26)
Sons's age = 14 + 12 = 26