1 volleyball is 38 yuan, 3 footballs are 135 yuan, how much is a volleyball cheaper than a football?
1只排球38元，3只足球135元，一只排球比一只足球便宜多少元？
<gadget id="calculator">135 / 3</gadget>
<output>45</output>

<gadget id="calculator">45 - 38</gadget>
<output>7</output>

<result>7</result>