Number of P-P bonds in H₃P₃O₉ is 'X'. Number of oxygen atoms around each 'P' atom in P₄O₆ is 'Y'

Sum of X and Y is

             H₃P₃O₉(cyclic trimeta Phosphoric acid)                                                

Number of  P-P bonds (X) = 0

P₄O₆

 No.of oxygen atoms around 'P' (Y) = 3

X+Y = (0+3) = 3