There is a job that C alone can complete in 10 hours, B and C can complete it in 4 hours, and A can complete the workload in 2 hours, and B can complete it in 3 hours. Now this job is done by C alone, he starts work at 5:00 in the morning and must finish at 12:00 noon. How many hours should A and B each help C to complete the task on time?
有一件工作，丙独做10小时完成，乙丙合做要4小时完成，甲在2小时内完成的工作量，乙需要3小时才能完成．现在这件工作由丙独做，他从早晨5时开始工作必须在中午12时完成．要使丙准时完成任务，甲、乙两人各应帮助丙工作几小时？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">12 - 5</gadget>
<output>7</output>

<gadget id="calculator">(1/10) * 7</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 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/4) - (1/10)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">3 / 2</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">(3/20) * (3/2)</gadget>
<output>9/40 = around 0.225</output>

<gadget id="calculator">(3/20) + (9/40)</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">(3/10) / (3/8)</gadget>
<output>4/5 = around 0.8</output>

<result>4/5 = around 0.8</result>