Mr. Wang bought 20 boxes of feed for 820 yuan. After going online, I found that the product was purchased directly from the manufacturer at 32 yuan per box. How much did he spend in total?
王先生用820元买了20箱饲料．上网后发现，该产品从厂家直接购货，每箱32元．他一共多花了多少钱？
<gadget id="calculator">20 * 32</gadget>
<output>640</output>

<gadget id="calculator">820 - 640</gadget>
<output>180</output>

<result>180</result>