Question

Frank is eight years older than her sister. In three years he will be twice as old as she is. How old are they now?

Answer 1

Frank is 13 and his sister is 5.

Explanation:
Frank’s age: y=x+8
After 3 years, their ages will be y=x+11 and his sisters age, y=x+3.
In 3 years he will be twice as old.
Equation:
x+11=2•(x+3) -> x=5
Frank is now 5+8=13.