Question

the present age of father is four times age of his son . four years later , he will be three times age of his son . find their present ages.

Answer 1

present age of son be x
present age of father be 4x
4 years later,
age of son =x+4
age of father=4x+4


but it is given that 4 years later father will have three times the age of his son
so,
4x+4=3(x+4)
4x+4=3x+12
x=8

so
present age of son is 8 yrs
present age of father is 8*4=32 yrs

Answer 2

Let the present age of the son be x years .
Then, age of the father is 4x years.
Four years later, 
age of son will be (x+4) years.
Then age of father will be (4x+4) years.
Acc. to the Question,
After 4 years, the age of father will be 3 times the son's age.
∴  4x+4 = 3(x+4)
  ⇒4x + 4 = 3x + 12
  ⇒4x - 3x = 12-4
  ⇒x = 8.
Hence, present age of son is x=8 years & the present age of father is 4x=4*8 years or 32 years.