Joe's age, Joe's sister's age and Joe's fathers age sums up to a century. When son is as old as his father, Joe's sister will be twice as old as now. When Joe is as old as his father then his father is twice as old as when his sister was as old as her father. Find age of each.
A. 20, 30, 50
B. 30, 20, 50
C. 25, 25, 50
D. 30, 15, 55

I think It would be Joe = 20, his sister = 30 and father = 50.