Uncle Wang bought 18 bags of feed for 900 yuan, but found out on the Internet that if he buys directly from the manufacturer, then each bag costs 45 yuan. How much does Uncle Wang spend per bag?
王叔叔用900元买了18袋饲料，结果在网上查询得知，如果从厂家直接进货，那么每袋是45元．王叔叔每袋多花多少钱？
<gadget id="calculator">900 / 18</gadget>
<output>50</output>

<gadget id="calculator">50 - 45</gadget>
<output>5</output>

<result>5</result>