Question 1129578
Sally is z year old,  given<br>

Jane is 2 years older than Sally —>  Jane is (z+2) years old  <br>

David is 4 times as old as Jane  (I reworded, the original wording didn't make sense) —>  David is 4*(z+2) years old<br>

These expressions relate the ages of Sally, Jane, and David by expressing those ages in terms of Sally's age.

I don't find any expression more useful than the other, perhaps Sally's age being z is simplest and easiest to work with.  For if someone tells you z they are giving you Sally's age straight away. <br> 

Sally: z
Jane: z+2
David:  4(z+2)