What is the answer to a+b=s+r; r

     " r  =  a  +  b  -  s "  .

Step-by-step explanation:

Given:  

a + b = s + r ;  Solve for:  "r" ;  that is; rewrite the equation in terms of:  " r " .

Subtract "s" from each side of the equation;  

   to isolate "r" on one side of the equation:

    →      a + b - s  =  s + r - s  ;

    →   to get:

   →       a + b - s  =  r  ;

 ↔   " r = a + b - s "  .

   →  which is the answer.

Hope this helps!

 Best wishes to you!