Let the age of the girl = x years.
So, the age of her younger sister = (x – 4) years.
Thus, the age of the brother = (x – 4 – 4) years = (x – 8) years.
According to question:
⇒ (x – 4) + (x – 8) = 16
⇒ x + x – 4 – 8 = 16
⇒ 2x – 12 = 16
Adding 12 to both sides, we get
⇒ 2x – 12 + 12 = 16 + 12
⇒ 2x = 28
Dividing both sides by 2, we get
⇒ 2x/2 = 28/2
⇒ x = 14
Thus, the age of the girl = x = 14 years,
The age of the younger sister = x – 4 = 14 – 4 = 10 years,
The age of the younger brother = x – 8 = 14 – 8 = 6 years.