The People's Liberation Army is performing a marching mission. The troops start from a certain place and travel 12 kilometers per hour. After 7 hours, the correspondent rides a motorcycle to catch up with the troops at a speed of 54 kilometers per hour to deliver orders. How long can the correspondent catch up with the troops?
解放军执行行军任务，部队从某地出发，每小时行12千米，7小时后通信员骑摩托车以每小时54千米的速度追赶部队传达命令，通信员几小时可以追上部队？
<gadget id="calculator">12 * 7</gadget>
<output>84</output>

<gadget id="calculator">54 - 12</gadget>
<output>42</output>

<gadget id="calculator">84 / 42</gadget>
<output>2</output>

<result>2</result>