Question

the sum of the age of father and son is 42 after 4 years the age of father will be 4 time the age of the son find their present age

Answer 1

Let the present age of son be x.
Then present age of father is 42-x.
After 4 years,
$(42 - x) + 4 = 4 \times (x + 4) \\ 46 - x = 4x + 16 \\ 5x = 30 \\ x = 6$
Therefore, age of son is 6 years
Age of father is 42-6 = 36 years