The return hall is 21m wide, and there are 6 slogans (without hanging at both ends); according to this calculation, the return hall is 30m long, how many slogans should be hung (without hanging at both ends)?
回报厅宽21m，挂有6幅标语(两端都不挂)；照这样计算，回报厅长30m，要挂多少幅标语(两端都不挂)？
<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<result>9</result>