Uncle Zhang’s family has 8 bags of chemical fertilizer, each bag weighs 50 kilograms, 315 kilograms are used up, how many kilograms are left?
张大伯家有8袋化肥，每袋重50千克，用去315千克，还剩多少千克？
<gadget id="calculator">50 * 8</gadget>
<output>400</output>

<gadget id="calculator">400 - 315</gadget>
<output>85</output>

<result>85</result>