Xiao Ming went up the mountain at 9:00 in the morning, walked 3 kilometers per hour, rested at the top of the mountain for an hour, then started to descend the mountain along the same road, walked 4 kilometers per hour, and arrived at the foot of the mountain at 1:30 in the afternoon. Ask him how many kilometers he walked in total.
小明上午九点上山，每小时走3千米，在山顶休息1小时后开始沿原路下山，每小时走4千米，下午一点半到达山下，问他共走了多少千米．
<gadget id="calculator">4.5 - 1</gadget>
<output>3.5</output>

<gadget id="calculator">3 + 4</gadget>
<output>7</output>

<gadget id="calculator">4 / 7</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">3.5 * (4/7)</gadget>
<output>2</output>

<gadget id="calculator">3 * 2 * 2</gadget>
<output>12</output>

<result>12</result>