Water is produced by hydrogen and oxygen at a mass ratio of 1:8. Now there are 50 kilograms of hydrogen, how much oxygen is needed to produce the corresponding amount of water?
水是由氢气和氧气1：8的质量比反映生成的，现在有50千克氢气，需要多少氧气才能生成相应量的水？
<gadget id="calculator">50 * 8</gadget>
<output>400</output>

<result>400</result>