Correct Option: B

Method 1
Let the present age of B and A be x and ( x + 9 ) years; then,
Age of B and A after 10 years will be x + 10 and x + 9 + 10;
According to question,
In 10 years A will be twice as old as B was 10 years ago
2(x - 10) = x + 9 + 10
2x - 20 = x + 19
⇒ 2x - x = 19 + 20
∴ x = 39 years

Method 2
Let us assume the present age of B and A be x and y years.
According to question,
A is now 9 years older than B,
y = x + 9...........(1)
Again according to question,
In 10 years A will be twice as old as B was 10 years ago
y + 10 = 2( x - 10)................. (2)
now put the value of y from equation (1) in above equation (2)
x + 9 +10 = 2x - 20
⇒ 2x - x = 19 + 20
⇒ x = 39 years
So Present age of B = 39 years.