Answer
If Christina's age is = x
Aaron's age is = x + 6
Jeo's age = 3(x + 6 )
So, the sum of their ages can be write as,

Also, they have given that the sum of their ages is 149
Therefore we can write a equation as,

Now let's solve this and find the age of Christina

Aaron's age is

Joe's age is

Hope this helps you.
Let me know if you have any other questions :-):-)