It takes 6 hours for A to type a manuscript alone, and 10 hours for B to type alone. Now A has been typing alone for several hours, and B continues to finish typing due to something, and it took 7 hours, so how many hours did A spend typing?
一份稿件，甲单独打字需6小时完成，乙单独打字需10小时完成．现在甲单独打若干小时后，因有事由乙接着打完，共用了7小时，那么甲打字用了多少小时．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">7 * (1/10)</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">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/6) - (1/10)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(3/10) / (1/15)</gadget>
<output>9/2 = around 4.5</output>

<result>9/2 = around 4.5</result>