Water is composed of hydrogen and oxygen in a mass ratio of 1:8. Now there are 72 kilograms of water, how many kilograms of oxygen are contained in this water?
水是由氢和氧两种元素按1：8的质量比化合而成的．现在有72千克的水，这些水中含有氧多少千克？
<gadget id="calculator">1 + 8</gadget>
<output>9</output>

<gadget id="calculator">8 / 9</gadget>
<output>8/9 = around 0.888889</output>

<gadget id="calculator">72 * (8/9)</gadget>
<output>64</output>

<result>64</result>