Dongfanghong Primary School has used 3,000kg of river sand for maintenance, and there are still 9 tons of river sand left. So how many kilograms of river sand did Dongfanghong Primary School have?
东方红小学进行维修，已经用了3000kg河沙，还剩下9吨河沙，那么东方红小学原来有多少千克河沙？
<gadget id="calculator">9 * 1_000</gadget>
<output>9_000</output>

<gadget id="calculator">9_000 + 3_000</gadget>
<output>12_000</output>

<result>12_000</result>