rectangular forest farm is 9 kilometers long. Uncle Wang rides a bicycle at a speed of 15 kilometers per hour to go around the forest farm. It takes 2 hours. How many square kilometers does the forest farm have?
一块长方形林场，长是9千米，王大爷骑自行车以每小时15千米的速度绕林场巡视一周，需要2小时，这个林场的面积有多少平方千米？
<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">15 * 1</gadget>
<output>15</output>

<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<gadget id="calculator">9 * 6</gadget>
<output>54</output>

<result>54</result>