At the exhibition of quality education achievements, 28 people from the calligraphy group of Century Primary School showed their specialties. How many people in the group performed the specialty demonstration?
在素质教育成果展示会上，世纪小学的书法小组有28人进行了特长展示，美术小组的人数是书法小组的(3/4)，合唱小组的人数是美术小组的(6/7)，合唱小组有多少人进行了特长展示？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">28 * (3/4)</gadget>
<output>21</output>

<gadget id="calculator">6 / 7</gadget>
<output>6/7 = around 0.857143</output>

<gadget id="calculator">21 * (6/7)</gadget>
<output>18</output>

<result>18</result>