At 20:30 on the evening of June 9th, a city suddenly had strong winds and heavy rain poured down. According to monitoring, within 1 hour, the city's rainfall reached 32.8 millimeters. Because the city's sewer drainage facilities are not perfect and scientific, many roads are flooded and traffic is paralyzed. For a section with serious water stagnation, if 17 sewers are used, the stagnant water can be drained in 30 hours; if 19 sewers are used, the stagnant water can be drained in 24 hours; there are several sewers in this road section, and after 6 hours of drainage, Due to the blockage of sediment and fallen leaves, the four sewers could not drain, and the remaining stagnant water took 2 hours to drain. How many sewers were there in this road section? (assuming rain falls at a uniform rate)
6月9日晚20时30分，某市突然狂风大作，暴雨倾盆而下．据监测显示，1小时内，该市降雨量达到32.8毫米．由于该市下水道排水设施不够完善科学，导致多处路面积水严重，交通瘫痪．某滞水严重的路段，若用17个下水道，30小时可将滞水排完；若用19个下水道，24小时可将滞水排完；该路段现有若干个下水道，排水6小时后，由于泥沙和落叶的堵塞，导致4个下水道不能排水，剩余的滞水花了2小时才排完，该路段原有多少个下水道？(假设雨水以均匀的速度下降)
<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">17 * 30</gadget>
<output>510</output>

<gadget id="calculator">19 * 24</gadget>
<output>456</output>

<gadget id="calculator">510 - 456</gadget>
<output>54</output>

<gadget id="calculator">30 - 24</gadget>
<output>6</output>

<gadget id="calculator">54 / 6</gadget>
<output>9</output>

<gadget id="calculator">30 * 9</gadget>
<output>270</output>

<gadget id="calculator">510 - 270</gadget>
<output>240</output>

<gadget id="calculator">6 * 9</gadget>
<output>54</output>

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

<gadget id="calculator">8 + 240 + 54 + 18</gadget>
<output>320</output>

<gadget id="calculator">6 + 2</gadget>
<output>8</output>

<gadget id="calculator">320 / 8</gadget>
<output>40</output>

<result>40</result>