A workshop of a toy factory needs to produce 900 toys. If it takes 20 hours to complete by hand, it only takes 4 hours to use a machine. The workers in the first workshop first make 5 hours by hand and then switch to machine production. How many hours will it take to complete? Task.
玩具厂一车间要生产900个玩具，如果用手工做要20个小时才能完成，用机器只需4小时，一车间工人先用手工做了5小时后改用机器生产，还需要多少小时才能完成任务．
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) * 5</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(3/4) / (1/4)</gadget>
<output>3</output>

<result>3</result>