Explanation:

Let's go through the problem step by step:

- Let the present age of the elder son be \( x \).

- Then, the father's present age will be \( 3x \) (as the father is three times the age of the elder son).

- For the younger son, let the age be \( y \). The elder child is 6 years older than the younger one, so \( x = y + 6 \).

- Four years hence, the father's age will be \( 3x + 4 \), and it is given that this age will be four times the age of the younger son at that time, i.e., \( 4(y + 4) \).

- Equating the above equations, we get: \( 3x + 4 = 4(y + 4) \).

Now, substituting \( x = y + 6 \) into the equation:

- \( 3(y + 6) + 4 = 4(y + 4) \)

- \( 3y + 18 + 4 = 4y + 16 \)

- Simplifying, we get: \( 3y + 22 = 4y + 16 \)

- Solving for \( y \), we find: \( y = 6 \).

Now, substituting back to find the father's age:

- \( x = y + 6 = 12 \)

- Father's age is \( 3x = 36 \).

Thus, the correct answer is:

- Option:1, 36 years