There is 15% salt water in a container. If 60 kg of water is added, the concentration of the salt water will become 5%. How many kg of salt water is in this container?
一容器内有浓度为15%的盐水，若再加入60千克水，则盐水的浓度变为5%，问这个容器内原来含盐多少千克？
<gadget id="calculator">0.15 - 0.05</gadget>
<output>0.1</output>

<gadget id="calculator">3 / 0.1</gadget>
<output>30</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">30 * (3/20)</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>