A boat sails from place A to place B, travels along the water, and travels 28 kilometers per hour. After arriving at place B, it turns back against the current and returns to place A. Traveling against the current takes 2 hours longer than traveling along the current. If the speed of the water is 4 kilometers per hour, how many kilometers are there between A and B?
一轮船从甲地开往乙地，顺水而行，每小时行28千米，到达乙地后又逆水返回，回到甲地；逆水比顺水多行2小时．如果水流速度是每小时4千米，那么甲、乙两地相距多少千米？
<gadget id="calculator">2 * 28</gadget>
<output>56</output>

<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">56 - 8 - 8</gadget>
<output>40</output>

<gadget id="calculator">1 / 28</gadget>
<output>1/28 = around 0.035714</output>

<gadget id="calculator">(1/28) * 4</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">(1/28) * 28</gadget>
<output>1</output>

<gadget id="calculator">(1/7) - 1</gadget>
<output>-6/7 = around -0.857143</output>

<gadget id="calculator">1 + (1/7) + (-6/7)</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">40 / (2/7)</gadget>
<output>140</output>

<result>140</result>