The x value :
In exchange 1 Q to R
In exchange 2 R to S
In exchange 3 R to Q
In exchange 4 Q to P
so x = 4
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The y value :
In exchange 1 P to Q
In exchange 2 Q to R
In exchange 3 R to S
In exchange 4 Q to R
In exchange 5 R to S
In exchange 6 R to Q
In exchange 7 S to Q
so y value = 7
x=4 & y=7 , option D .