The machinery factory has two lathes to make parts. The first one takes 1.5 hours to make 21 parts, and the second one takes 2.4 hours to make 36 parts. Now the two lathes can make 464 parts at the same time. How many hours will it take to complete?
机械厂有两台车床做零件，第一台做21个零件需1.5小时，第二台做36个零件需2.4小时，现在两台机床同时做464个零件，需几小时才完成？
<gadget id="calculator">21 / 1.5</gadget>
<output>14</output>

<gadget id="calculator">36 / 2.4</gadget>
<output>15</output>

<gadget id="calculator">14 + 15</gadget>
<output>29</output>

<gadget id="calculator">464 / 29</gadget>
<output>16</output>

<result>16</result>