If A works alone for 63 days, then B can complete it in 28 days alone; if they cooperate, they can complete it in 48 days. Now B works alone for 84 days. So how many days will A have to do alone to complete the whole project?
某工作甲独做63天后乙再独做28天可完成；若两人合作，则48天完成．现乙独做84天．那么甲单独还要做多少天才能完成全部工程？
<gadget id="calculator">1 / 48</gadget>
<output>1/48 = around 0.020833</output>

<gadget id="calculator">(1/48) * 28</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">(1/112) * 84</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) / (1/84)</gadget>
<output>21</output>

<result>21</result>