Prove if x%9 + y%9 + z%9 = 0 or 9 , xyz % 9 = 0 or 9

x % 9 = 100x % 9;
y % 9 =10y % 9;

100x % 9 + 10y % 9 + z % 9 = 0 or 9

xyz % 9 = 0 or 9

4 % 9 + 3 % 9 + 2 % 9 = 9;

432 % 9 = 0;