Xiaohong travels back and forth between the East and West villages. She travels an average of 5 kilometers per hour when she goes there. She walks for 3 hours to reach the West Village. When she returns, she travels an average of 7.5 kilometers per hour. The average speed of Xiaohong’s travel between the East and West villages is How many kilometers per hour.
小红往返于东、西两村，去时平均每小时走5千米，走了3小时到达西村，返回时，平均每小时走7.5千米，小红往返东、西两村的平均速度是每小时走多少千米．
<gadget id="calculator">5 * 3 * 2</gadget>
<output>30</output>

<gadget id="calculator">3 / 7.5</gadget>
<output>0.4</output>

<gadget id="calculator">5 * 0.4</gadget>
<output>2</output>

<gadget id="calculator">3 + 2</gadget>
<output>5</output>

<gadget id="calculator">30 / 5</gadget>
<output>6</output>

<result>6</result>