Given the average age of couple and their son = 40

=> Sum of age (H +W +S) = 40×3

Let the age of daughter in law at the time of marriage = D years

Now after 10 years,

(H + S +W) + 3×12 + D +12 + 10 = 38×5

178 + D = 190

D = 190 -178 = 12 years

Let Ishika and her daughter present ages be p and q

 From the given data, 

p = 4/3(p - 9)

 => p = 36 years 

Hence, Ishika's present age = 36 years and

Her daughter's present age = 1/6 x 36 = 6 years 

Now, required her daughter?s age three years ago = 6 - 3 = 3 years.

Let number of boys = x  , Let number of girls = y
Total numbers of students = x + y
(x + y) × 15.8 = 16.4x + 15.4y
0.6x = 0.4y
x/y = 0.4/0.6 = 2/3

 Ratio of boys and girls in the class is 2:3

Let Anushka age = X
Charu latha 12 yrs older than Anushka so Charu latha age = x+12
Kajal is thrice as old as Anushka so Kajal age = 3x
The ages of Anushka, Kajal and Charu latha together are 57 years
i.e x + (x+12) + 3x = 57
=> 5x = 45
:- x = 9
Anushka age = 9
Kajal age = 3x = 27
Charu latha age = x+12 = 21

Let the age of the daughter today be ?x? years.
Mother?s age today = 3x years
After 10 years, we have
3x + 10 = 2(x + 10)
x = 10 years.

Raj Tarun's age = 0 when he was born.
Then, given his brother is 6 years old.
Then his father is 6 + 32 = 38 when Raj Tarun was born
And his mother is 3 years yonger than his father => so his mother was 35 years old when Raj Tarun was born
and his sister is 25 year younger than his mother
so Raj Tarun's sister was 10 years old when Raj Tarun was born.

Let the mother's present age be x years.

Then, the person's present age = 2/5 x years.

(2x/5 + 8) = 1/2 (x + 8)

2(2x + 40) = 5(x + 8) => x = 40.

Let present Anirudh's age be 'A' and Bhavana's age be 'B'

Given seven years, their ratio is 7:9

=> A-7 : B-7 = 7 : 9

=> 9A - 7B = 14 .......(1)

And given,

Chandhu is 12 years older than A nad 12 years younger than B

=> C = A + 12....(2)

=> B = C + 12

=> B = A + 12 + 12 .....(From (2))

=> B = A + 24 ....(3)

Put (3) in (1)

9A - 7(A+24) = 14

9A - 7A - 168 = 14

2A = 182

=> A = 91 years

=> C = A + 12 = 91 +12 = 103 years.

According to the given data,

P + Q = 41 ......(1)

R - 1 = P + 2

R = P + 3

and

P + 4 = Q - 1

=> Q = P + 5 ....(2)

From (1)&(2)

P = 18

Q = 18 + 5 = 23

R = 18 + 3 = 21

=> P/S = 3/4

=> S = 4/3 x 18 = 24

Required Difference = S - R = 24 - 21 = 3.

Let Hari Ram's present age = x

Then, his son's age = x/3

Father's age = 5x/2

$$\begin{gathered} x + x 3 + 5 2 x 3 = 46 \\ = > x = 36 yrs \end{gathered}$$

Now the required difference =  5 2 x 36 - 36 3 = 78 yrs