The passenger car and the truck depart from the two cities A and B at the same time, facing each other. The bus meets the truck at 20 kilometers from the midpoint of the two cities. After meeting, the truck continues to move forward at the original speed of 40 kilometers per hour, After 3.5 hours to reach city A, how many kilometers per hour will the bus travel?
客车和货车同时从A、B两城分别开出，相对而行，客车驶过两城中点20千米处与货车相遇，相遇后，货车仍以原来每小时40千米的速度继续前进，再经过3.5小时到达A城，客车每小时行多少千米？
<gadget id="calculator">40 * 3.5</gadget>
<output>140</output>

<gadget id="calculator">140 - 20</gadget>
<output>120</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">120 / (1/2)</gadget>
<output>240</output>

<gadget id="calculator">240 - 140</gadget>
<output>100</output>

<gadget id="calculator">100 / 40</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">140 / (5/2)</gadget>
<output>56</output>

<result>56</result>