At 12:00 noon, the car departs from point A to point B at a speed of 40 kilometers per hour. At the same time, the large truck departs from point B to point A. When the car reaches point A, it immediately turns around and increases its speed to The original double, and finally caught up with the truck at the midpoint of the two places. It was 7 pm at this time. May I ask: how many kilometers per hour is the speed of the big truck?
中午12点时，小轿车从A地出发B地，速度是每小时40千米，同时大卡车从B地出发去A地，当小轿车到达A地时，立即掉头行驶，并且将速度提高到原来的2倍，最终在两地中点处追上了卡车，此时是下午7点，请问：大卡车的速度是每小时多少千米？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * (1/2)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">7 / (5/4)</gadget>
<output>28/5 = around 5.6</output>

<gadget id="calculator">40 / 2 / 7</gadget>
<output>20/7 = around 2.857143</output>

<gadget id="calculator">(28/5) * (20/7)</gadget>
<output>16</output>

<result>16</result>