Teacher Wang bought a 30-meter-long rope and used it (3/4) to make 6 skipping ropes. How many meters are left useless?
王老师买来一根长30米绳子，用它的(3/4)做了6根跳绳，还剩下多少米没有用？
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">30 * (1/4)</gadget>
<output>15/2 = around 7.5</output>

<result>15/2 = around 7.5</result>