There are some steel products in a certain warehouse, 20% of the total amount was used for the first time, 30% more than the first time was used for the second time, 4.5 tons more than the first time was used for the second time, how much was used for the first time tons of steel?
某仓库里有一些钢材，第一次用去总数的20%，第二次用去的比第一次多总数的30%，第二次比第一次多用4.5吨，第一次用去多少吨钢材？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">4.5 / (3/10)</gadget>
<output>15</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 * (1/5)</gadget>
<output>3</output>

<result>3</result>