A train travels from City A to City B, traveling 120 kilometers per hour, and can arrive in 4.5 hours. When returning, it speeds up, and it takes half an hour less. What is the speed when returning?
火车从甲城开往乙城，每小时行120千米，4.5小时能到达，回来时提速，少用了半小时，回来时的速度是多少？
<gadget id="calculator">120 * 4.5</gadget>
<output>540</output>

<gadget id="calculator">4.5 - 0.5</gadget>
<output>4</output>

<gadget id="calculator">540 / 4</gadget>
<output>135</output>

<result>135</result>