Can someone me i got these three questions wrong

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.

These are the multiples of 15 but what you are probably asking or what are the factors of 15