The ages of three siblings total 21 years. The middle child is one year older than the youngest, and the eldest is three times as old as the yougest. How old is each child ? ( show work )

Let y be age of youngest.

y + (y + 1) + 3y = 21

5y + 1 = 21

5 y = 20

y = 4. Age of youngest

y + 1 = 5. Age of middle child

3y = 12. Age of oldest child.