It takes 10 hours for team A to complete a project alone, and 15 hours for team B to complete the project in 9 hours, and it is required that one of the teams do it first, and then the two teams work together. How many hours is the minimum required?
一项工程，单独完成甲队要10小时，乙队要15小时，既要在9小时完成这项工程，而且要求先由其中一队先做，再两队合做，那么两队合做的进间至少要多少小时？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 9</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/10) / (1/15)</gadget>
<output>3/2 = around 1.5</output>

<result>3/2 = around 1.5</result>