Build a highway. If A, B, and C cooperate, the project can be completed in 90 days; if A, B, and D cooperate, the project can be completed in 120 days; if C, D cooperate, the project can be completed in 180 days. If A and B cooperate for 36 days, and A, B, C and D cooperate to complete the rest of the project, how many days will it take to complete the project?
修一条高速公路．若甲、乙、丙合作，90天可完工；若甲、乙、丁合作，120天可完工；若丙、丁合作，180天完工．若甲、乙合作36天后，剩下的工程由甲、乙、丙、丁合作，还需要多少天完工？
<gadget id="calculator">1 / 90</gadget>
<output>1/90 = around 0.011111</output>

<gadget id="calculator">1 / 120</gadget>
<output>1/120 = around 0.008333</output>

<gadget id="calculator">1 / 180</gadget>
<output>1/180 = around 0.005556</output>

<gadget id="calculator">(1/90) + (1/120) + (1/180)</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/40) / 2</gadget>
<output>1/80 = around 0.0125</output>

<gadget id="calculator">(1/80) - (1/180)</gadget>
<output>1/144 = around 0.006944</output>

<gadget id="calculator">36 * (1/144)</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">(3/4) / (1/80)</gadget>
<output>60</output>

<result>60</result>