A, B, and C set off at the same time and at the same place, and chase Zhang Hua along the same route. The three catch up with Zhang Hua in 9 minutes, 15 minutes, and 18 minutes respectively. A's speed is 240m/mn, and B's speed is 200m /m m, find the speed of C?
甲、乙、丙三人同时、同地点出发，沿同一路线追张华，三人分别用9分钟、15分钟、18分钟追上张华，甲的速度为240m/米n，乙的速度200m/米m，求丙的速度？
<gadget id="calculator">200 * 15</gadget>
<output>3_000</output>

<gadget id="calculator">240 * 9</gadget>
<output>2_160</output>

<gadget id="calculator">3_000 - 2_160</gadget>
<output>840</output>

<gadget id="calculator">15 - 9</gadget>
<output>6</output>

<gadget id="calculator">840 / 6</gadget>
<output>140</output>

<gadget id="calculator">140 * 18</gadget>
<output>2_520</output>

<gadget id="calculator">140 * 9</gadget>
<output>1_260</output>

<gadget id="calculator">2_160 - 1_260</gadget>
<output>900</output>

<gadget id="calculator">2_520 + 900</gadget>
<output>3_420</output>

<gadget id="calculator">3_420 / 18</gadget>
<output>190</output>

<result>190</result>