For a project, A and B cooperate to complete the entire project (7/10) in 3 days, and then A alone completes the rest. A has done a total of 10.5 days. How many days will it take if A alone completes this project?
一项工程，先由甲、乙合作3天完成全部工程的(7/10)，再由甲单独完成剩下的，甲一共做了10.5天．这项工程如果由甲单独完成需要多少天．
<gadget id="calculator">7 / 10</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">1 - (7/10)</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">10.5 - 3</gadget>
<output>7.5</output>

<gadget id="calculator">(3/10) / 7.5</gadget>
<output>0.04</output>

<gadget id="calculator">1 / 0.04</gadget>
<output>25</output>

<result>25</result>