Dad is 0.52 meters taller than Xiaohong, and 0.21 meters taller than mother. How much is mother's height taller than Xiaohong?
爸爸的身高比小红高0.52米，比妈妈的身高高0.21米，妈妈的身高比小红高多少米？
<gadget id="calculator">0.52 - 0.21</gadget>
<output>0.31</output>

<result>0.31</result>