5, six years younger to him.Age of grandson = 6 + 5 = 11 yearsIf 4 years are subtracted from the age of a person and divided by 5, the result gives hisgrandson's age.According to question:(x – 4) ÷ 5 = 11⇒ (x – 4) = 55⇒ x = 59Hence, the grandfather is 59 years old.