Mr((NH4)2SO4) = 14*2 + 1*8 + 32+16*4 =132
W(N) = Ar(N) *n / Mr(NH4)2SO4 *100% = 14*2 / 132 *100% =21%
W(H) = Ar(H) *n / Mr(NH4)2SO4 *100% = 1*8 / 132 *100% = 6%
W(S) = Ar(S) *n / Mr(NH4)2SO4) *100% = 32*1 / 132 *100% =24%
W(O) = Ar(O) *n / Mr(NH4)2SO4) *100% = 16*4 / 132 *100% = 48%