It is 155 kilometers from place A to place B. A car drives from place A to place B. The first section is on a flat road and travels 35 kilometers per hour. The second section is uphill and travels 30 kilometers per hour. The section is going down the mountain, traveling 40 kilometers per hour. It is known that the downhill road is 20 kilometers. The car travels from A to B in a total of 4.5 hours. How many kilometers is the flat road?
从甲地到乙地155千米，一辆汽车从甲地开往乙地，第一段为平路，每小时行35千米，第二段为上山，每小时行30千米，第三段为下山，每小时行40千米，已知下山路20千米，汽车从甲地到乙地共行驶4.5小时，平路长多少千米？
<gadget id="calculator">135 / 30</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">20 / 40</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) - 4.5</gadget>
<output>-4</output>

<gadget id="calculator">(9/2) + (-4)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">1 / 35</gadget>
<output>1/35 = around 0.028571</output>

<gadget id="calculator">(1/30) - (1/35)</gadget>
<output>1/210 = around 0.004762</output>

<gadget id="calculator">(1/2) / (1/210)</gadget>
<output>105</output>

<result>105</result>