Hi William,
I'll walk you through the steps you need, in order to solve this, but not give the answer outright.
So, because you don't know the ages, you have unknown numbers, which definitely means Algebra!
The question mentions a sum. If you remember, sum means addition. So, in order to be able to find the algebra equation for the sum of their ages, you should use the same variable when you're algebraically defining both of them.
Let's use the variable E for Eric's age.
Then, because Eric's Dad is 28 years older than Eric, algebraically you can express Eric's Dad's age as (E+28).
The sum of their ages is 64. Like I said a few lines above, sum means addition.
So the sum of their ages, using algebra, would be Eric's age plus his Dad's age.
Eric's age + Eric's Dad's age = 64.
If you use the equation directly above, and substitute in the variable expressions I mentioned above, you should be able to solve for Eric's age. Then after solving for Eric's age, you'll be able to solve for Eric's Dad's age.
Good luck!
