Potential energy, though this seems like a question for the science section unless I'm missing something.
Your function is:
Y= 29 + 0.35x
X represents the money that Tracy is charged per minute
<u>Answer</u>
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 :-):-)