Mom is exercising, and it is (21/5) kilometers to walk along Huanhu Road. It took (12/5) hours for my mother to walk 2 laps. Do the math, how many kilometers does my mother walk on average per hour?
妈妈锻炼身体，沿着环湖路走一圈是(21/5)千米．妈妈走2圈用了(12/5)小时．算一算，妈妈平均每小时走多少千米？
<gadget id="calculator">21 / 5</gadget>
<output>21/5 = around 4.2</output>

<gadget id="calculator">12 / 5</gadget>
<output>12/5 = around 2.4</output>

<gadget id="calculator">2 / (12/5)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">(21/5) * (5/6)</gadget>
<output>7/2 = around 3.5</output>

<result>7/2 = around 3.5</result>