There is no need to use Union operator here.
Just because they say you can use operators from $(∪, −)$ we don't need to use both of them.
Also they are saying that only the minimum number of operators from (∪, −) which is equivalent to $R ∩ S$.
My expression is Minimal.
Yes @Deepak Poonia Sir I have edited my comment.
$R \cap S = S – ( R – (R \cup S) ) $ is Incorrect.
$S = S – ( R – (R \cup S) ) .$
Can you please say Is it necessary to use both U,-?
Can I represent R ∩ S=R-(U-S) ?
where U is the universal set.
Question says only the minimum number of operators from (∪, −) which is equivalent to R ∩ S. Using union is unnecessary here !
Thanks for this solution
An other approach
((R ∪ S-(R-S))-(S-R))