Let c represent Christina's age.
Then (c+6) represents Aaron's age.
And 3(c+6) represents Joe's age.
The sum of their ages is then ...
... c + (c+6) +3(c+6) = 149 . . . . . the sum given in the problem statement
... 5c +24 = 149 . . . . . . . . . . . . . eliminate parentheses, collect terms
... 5c = 125 . . . . . . . . . . . . . . . . . subtract 24
... c = 25 . . . . . . . . . . . . . . . . . . . divide by 5. Christina's age
... c+6 = 31 . . . . . . . . . . . . . . . . . Aaron's age
... 3·31 = 93 . . . . . . . . . . . . . . . . Joe's age
Joe is 93, Aaron is 31, Christina is 25.
