Lian is 12 years old and Ella is 8 years old.
Lian and her younger sister Ella are 4 years apart.
The sum of their ages is 20.
Let L be Lian’s age in years.
Let E be Ella’s age in years.
The system of linear equations that models the scenario is:
Putting L=E+4 in the second equation
Now we have , L+E=20
Therefore, Lian is 12 years old and Ella is 8 years old.