Uncle Fei drove home, originally planning to drive at a speed of 40 km/h. Halfway through the journey, the previous speed was only 30 km/h, so what speed must be reached in the second half of the journey to get home on time?
费叔叔开车回家，原计划按照40千米/时的速度行驶．行驶到路程的一半时发现之前的速度只有30千米/时，那么在后一半路程中，速度必须达到多少才能准时到家？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) * 120</gadget>
<output>60</output>

<result>60</result>