Sometimes soaking seeds in salt water can promote a good harvest of crops. According to the mass ratio of salt and water is 3:100 preparation of brine. How many kilograms of salt is needed for a sub-station to prepare 618kg of this brine?
有时用盐水浸种可以促进农作物丰收．按盐与水的质量比是3：100配制盐水．某种子站要配制618kg这种盐水，需要食盐多少千克？
<gadget id="calculator">3 + 100</gadget>
<output>103</output>

<gadget id="calculator">618 / 103</gadget>
<output>6</output>

<gadget id="calculator">6 * 3</gadget>
<output>18</output>

<result>18</result>