Present age of Jacob be ‘x’.

His son’s present age is ‘y’.

After 5 years, Age of Jacob will be x + 5

After 5 years, Age of his son will be y + 5

At that time Jacob’s age will be three times that of his son.

x + 5 = 3(y + 5)

x + 5 = 3y + 15

x – 3y = 15 – 5

x – 3y = 10 ………… (i)

5 years ago Jacob’s age was x – 5

5 years ago, age of Jacob’s son was y – 5

At that time Jacob’s age was seven times that of his son.

∴ x – 5 = 7(y – 5)

x – 5 – 7y – 35

x – 7y = -35 + 5

x – 7y = -30 ………….. (ii)

From eqn. (i),

x – 3y = 10

x = 10 + 3y

Substituting the value of ‘x’ in eqn. (ii),

x – 7y = -30

10 + 3y – 7y = -30

10 – 4y = -30

-4y = -30 – 10

-4y = -40

∴ y = \(\frac{40}{4}\)

∴ y = 10

Substituting the value of ‘y’ in

x = 10 + 3y

= 10 + 3 × 10

= 10 + 30

∴ x = 40

∴ Present age of Jacob is 40.

Present age of Jacob’s son is 10 .