There are 25 pipes A and B. It is known that the length of each pipe of type A is 8 meters, and the length of each pipe of type B is 5 meters. The total length of pipe A is 21 meters shorter than that of pipe B.
甲、乙两种管子共25根，已知甲种管每根长8米，乙种管每根长5米，甲种管比乙种管总长短21米，甲种管子有多少根．
<gadget id="calculator">200 + 21</gadget>
<output>221</output>

<gadget id="calculator">5 + 8</gadget>
<output>13</output>

<gadget id="calculator">221 / 13</gadget>
<output>17</output>

<gadget id="calculator">25 - 17</gadget>
<output>8</output>

<result>8</result>