Lana is the oldest of four sisters. her youngest sister is half her age. the other two sisters are twins $2$ years younger than lana. when the four sisters' ages are added together, the result is $45$. if the youngest sister is $n$ years old, what is $n$? lana is the oldest of four sisters. her youngest sister is half her age. the other two sisters are twins $2$ years younger than lana. when the four sisters' ages are added together, the result is $45$. if the youngest sister is $n$ years old, what is $n$?