If Potassium has a charge of 1, and chlorate is ClO3 with again a charge of one, you just put them together. You have KCLO3. When it is heated, it gives off potassium chloride and oxygen, chloride also having a 1 charge. Because both charges are 1, it becomes KCl, and oxygen is just O2. Put this all together and you have KClO3=KCl+O2. Balance the equation (2KClO3=2KCl+3O2) and you have your answer. Hope this helps.