The correct option is B 90 years
Let the present age of Sam be x years and the age of his son be y years.
Presently, the age of Sam is six times the age of his son.
Hence, x = 6y...(1)
After ten years, age of Sam will be (x+10) years and the and the age of his son will be (y+10) years.
According to the question, ten years later, the age of Sam will be four times the age of his son.
Hence, (x+10) = 4(y+10)...(2)
Substituting the value of x from (1) in (2),
(6y + 10) = 4y + 40
2y = 30
y = 15
we get y = 15 and x = 90.
Hence, the present age of Sam is 90 years.