Xiao Ming goes to climb a mountain. He starts climbing at 7:00 in the morning and reaches the top of the mountain at 9:00 am. It is known that the distance from the bottom of the mountain to the top of the mountain is 18 kilometers. How many kilometers does Xiao Ming walk on average per hour?
小明去爬山，早上7：00开始爬山，上午9：00到达山顶，已知山下到山顶共18千米，小明平均每小时走多少千米？
<gadget id="calculator">9 - 7</gadget>
<output>2</output>

<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<result>9</result>