Janet is three years older than her little sister Julie. Janet's brother is eight years younger their their sister Julie. The sum of all of their ages is 55 years. ***Linear equation***
Let Julie’s age be x years, then Janet=x+3, brother=x-8. x+x+3+x-8=55, 3x-5=55, 3x=60, x=20. The ages are Julie is 20, Janet is 23 and their brother is 12.