We know that Frank is 1/4 Dana's age, so if Frank is represented by f, and Dana is represented by d, then the equation would be
1/4d = f
Secondly, we know that Neil's age is one-half the difference between Dana's and Frank's ages. Because of we learned that Frank is a fraction of Dana's age, we can infer that he is younger than Dana. So, if Neil's age is represented by the variable n, then the equation would be
1/2(d - f) = n
Finally, if we know that Dana is 16 years old, we can find out the other siblings ages using the equations we made above.
d=16
1/4d = f
1/4(16) = f
4 =f
1/2(d - f) = n
1/2(16-4) = n
1/2(12) = n
6=n
Therefore, Frank is 4 years old and Neil is 6 years old.