The process needs to spend 'r' units of time in CPU. But since this is a question of round robin scheduling, it has to switch between run and ready state after spending every 'q' units in CPU. Suppose it has do 'n' switches. So in order to complete 'r' units, r=nq gives n=(r/q) no. of switches.
Now, after every 'q' comes the time spent on context switching which is 's'. So n*s times wasted for this purpose.
Time utilized in CPU is 'r' (or nq, its the same thing).
Total time needed for this process to complete is r+ns (or you can write n(q+s) ).
CPU utilization is = r/(r+ns)
Replace n with r/q and you will get Option A.