Teams A, B, and C have to complete two projects A and B, and the workload of project B is increased by (1/4) the workload of project A. If teams A, B, and C are allowed to work independently, the time required to complete project A is 20 days, 24 days, and 30 days, respectively. Let team A do project A, and team B work on project B. In order to complete these two projects at the same time, team C cooperates with team B to do project B for a few days, and then cooperates with team A to do project A for a few days. How many days did Team C and Team B work together?
甲、乙、丙三队要完成A，B两项工程，B工程的工作量是A工程工作量再增加(1/4)．如果让甲、乙、丙三队单独做，完成A工程所需时间分别是20天、24天、30天．现在让甲队做A工程，乙队做B工程，为了同时完成这两项工程，丙队先与乙队合做B工程若干天，然后再与甲队合做A工程若干天．问丙队与乙队合做了多少天？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 24</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">1 + 1 + (1/4)</gadget>
<output>9/4 = around 2.25</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) + (1/24) + (1/30)</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(9/4) / (1/8)</gadget>
<output>18</output>

<gadget id="calculator">(1/24) * 18</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(1/4) - (3/4)</gadget>
<output>-1/2 = around -0.5</output>

<gadget id="calculator">1 + (-1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / (1/30)</gadget>
<output>15</output>

<result>15</result>