P = 4 , O = 6 + H = 12 , O = 6 (in the left side ) and which equals to .....H = 4*3= 12 , P = 4*1 = 4 , O = 4 *3= 12 (it has to be O3 to be balanced - 4H3PO3) - P in the left side 4 the same as the right - O 12 in the left the same goes for the right -H 12 in the left and 12 in the right