Mr((NH4)3PO4) = 14*3 + 1*12 + 31 + 16*4 = 149
W(N) = Ar(N) * n / Mr(NH4)3PO4 *100% = 14*3 / 149 *100% =28%
W(H) = Ar(H) * n / Mr(NH4)3PO4 *100% = 1*12 / 149 *100% = 8%
W(P) = Ar(P) *n / Mr(NH4)3PO4 *100% = 31 *1 / 149 *100% = 21%
W(O) = Ar(O) * n / Mr(NH4)3PO4 *100% = 16*4 / 149 *100% = 43%