Xiao Ming's weight is 50 kg, which is 20 kg heavier than Xiao Hong's. How much is Xiao Hong's weight in kg?
小明的体重是50千克，比小红重20千克，小红的体重是多少千克？
<gadget id="calculator">50 - 20</gadget>
<output>30</output>

<result>30</result>