The coal station originally had several tons of coal. 450 tons were transported in the first time, half of the existing coal was transported in the second time, and the remaining coal was 600 tons. How many tons of original coal?
煤站原有煤若干吨．第一次运进450吨，第二次运出现有煤的一半，结果剩余的煤是600吨．原有煤多少吨？
<gadget id="calculator">600 * 2</gadget>
<output>1_200</output>

<gadget id="calculator">1_200 - 450</gadget>
<output>750</output>

<result>750</result>