This winter, the boiler room plans to burn several tons of coal for heating. If the existing coal is calculated as 5.5 tons per day, there will be 90 tons of coal remaining, and if it is calculated as 6 tons per day, there will be 30 tons left. Question: How many tons of existing coal are there?
今年冬天锅炉房计划烧若干吨煤供应暖气，现存的煤如果按每天用5.5吨计算可剩余90吨煤，如果按每天用6吨计算则可剩余30吨．问：现存煤有多少吨？
<gadget id="calculator">90 - 30</gadget>
<output>60</output>

<gadget id="calculator">6 - 5.5</gadget>
<output>0.5</output>

<gadget id="calculator">60 / 0.5</gadget>
<output>120</output>

<gadget id="calculator">5.5 * 120</gadget>
<output>660</output>

<gadget id="calculator">660 + 90</gadget>
<output>750</output>

<result>750</result>