A project can be completed by A alone for 63 days, and then by B alone for 28 days. If A and B cooperate, it will take 48 days to complete. Now A will do it alone for 42 days first, and then B will complete it alone, how many more days will be needed.
某工程先由甲单独做63天，再由乙单独做28天即可完成．如果由甲、乙两人合作，需48天完成．现在甲先单独做42天，然后再由乙来单独完成，那么还需要做多少天．
<gadget id="calculator">42 / 84</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 48</gadget>
<output>1/48 = around 0.020833</output>

<gadget id="calculator">28 / 48</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">1 - (7/12)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">63 - 28</gadget>
<output>35</output>

<gadget id="calculator">(5/12) / 35</gadget>
<output>1/84 = around 0.011905</output>

<gadget id="calculator">(1/48) - (1/84)</gadget>
<output>1/112 = around 0.008929</output>

<gadget id="calculator">(1/2) / (1/112)</gadget>
<output>56</output>

<result>56</result>