(1) The present age of a father is three times that of his elder son.
Let the present age of father be F and that of elder son's be E, then:
F = 3 × E (2) Four years hence, the age of the father will be four times that of his younger son.
Let the present age of younger son be Y, then:
F + 4 = 4 × (Y + 4) (3) If the difference between the present ages of the elder and younger child is 6 years, then:
E - Y = 6 ⇒ E = Y + 6, From above three statements,
⇒ F = 3Y + 18 (from (1) and (3))
⇒ Y = (F - 18) ÷ 3
Now, substituting Y in (2)
⇒
F+4=4×[+4] ⇒
+1=−6+4 ⇒
−=3 ⇒ F = 3 × 12
⇒ F = 36
Hence, the present age of father is 36 years.