The school bought 30 basketballs and 16 footballs. If you buy 4 more badmintons, it will be as many as the sum of basketballs and footballs. How many badmintons do you buy?
学校买来篮球30个，足球16个．如果买的羽毛球再添4个就与篮球和足球的个数和同样多．买羽毛球多少个？
<gadget id="calculator">16 - 4</gadget>
<output>12</output>

<gadget id="calculator">30 + 12</gadget>
<output>42</output>

<result>42</result>