Answer: 20 years old
Step-by-step explanation: So, we know the girl is 4 years older than the sister...how do we know that? Because...
6 - 2 = 4
She's 4 years older...we know the girl is 24, then the sister must be 20.
24 - 4 - 20...
The sister is 20 years old, I hope this helps