you first use the amount it gives you. then you need to use a ratio from your balanced equation so 1.65moles of KCLO3 is what you would put first. then look back at the equation to find what you need to put on the bottom. 1.65 mol KCLO3= 2 mol KCLO3. then you know 2 mol KCLO3 is = to 3 mol O2. then just multiply across and divide by what’s underneath to find moles of O2. you should get 2.475 moles of O2