$R-(R-S)$

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.

@Abhrajyoti00

$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 !

@Rajarshi Sarkar Thanks for this solution

An other approach

((R ∪ S-(R-S))-(S-R))