Let son's age 5 years hence = x years
Then, father's age after 5 years hence = 3x years
∵ 7(x - 10) = (3x - 10)

Correct Option: B

Let son's age 5 years hence = x years
Then, father's age after 5 years hence = 3x years
∵ 7(x - 10) = (3x - 10)
⇒ x(7 - 3) = 70 - 80
⇒ x = 15
∴ Father's present age = (3x - 5) = 40 years

Let Arvind's present age be x years
Then, his father's present age = 4x years
∵ (4x - 5) = 7(x - 5)

Correct Option: B

Let Arvind's present age be x years
Then, his father's present age = 4x years
∵ (4x - 5) = 7(x - 5)
⇒ 3x = 30
∴ x = 10
Hence, Arvind's father's age is 40 years.

Let the present age of the elder person be x years.
Then, the present age of the younger person = (x - 10) years.
∵ (x - 15) = 2(x - 10 - 15)

Correct Option: B

Let the present age of the elder person be x years.
Then, the present age of the younger person = (x - 10) years.
∵ (x - 15) = 2(x - 10 - 15)
⇒ x = 35
∴ the present age of the elder person is 35 years.

Let the daughter's present be x years.
Then, mother's present age = (50 - x) years
Now, 7(x -5) = (50 - x - 5)

Correct Option: C

Let the daughter's present be x years.
Then, mother's present age = (50 - x) years
Now, 7(x -5) = (50 - x - 5)
⇒ x = 10
So, the present ages of mother and daughter are 40 years and 10 years respectively.

Let Kamla's age 6 years ago be x years.
So, Kamla's present age = (x + 6) years
∴ x + 6 = 5x / 4

Correct Option: B

Let Kamla's age 6 years ago be x years.
So, Kamla's present age = (x + 6) years
∴ x + 6 = 5x / 4
⇒ 4x + 24 = 5x
⇒ x = 24
So, Kamla's Present age = (x + 6) years = 30 years
∴ Son's present age = 30/10 = 3 years