It takes 30 days for a canal to be repaired by Team A, but it only takes 20 days for Team A and Team B to repair it together. Now the two teams will work together for 4 days, and the rest will be done by team A. How many days will it take for team A to finish?
一条水渠，由甲队来修要用30天完成，由甲、乙两队合修只需20天．现先由两队合修4天，余下的全由甲队来修，甲队还需多少天才能完成？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) * 4</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(4/5) / (1/30)</gadget>
<output>24</output>

<result>24</result>