Verified answer

Mr(K3PO4) = 39*3 + 31 + 16*4 =212

W(K) = Ar(K) * n / Mr(K3PO4)  *100% = 39*3 / 212  *100% =55%

W(P)= Ar(P) * n / Mr(K3PO4)  *100% = 31*1 / 212  *100% =15%

W(O) = Ar(O) * n / Mr(K3PO4)  *100% = 16*4 / 212 *100% =30%