There are three pools A, B, and C with the same capacity. A type A pump alone injects water into pool A, a type B pump independently injects water into pool B, and a type A and a type B pump together inject water into pool C. It is known that it takes 4 hours longer to fill pool B than pool C, and it takes 5 hours longer to fill pool A than pool B, how many hours will it take to fill two-thirds of pool C ．
现有甲、乙、丙三个容量相同的水池．一台A型水泵单独向甲水池注水，一台B型水泵单独向乙水池注水，一台A型和一台B型水泵一起向丙水池注水．已知注满乙水池比注满丙水池所需时间多4个小时，注满甲水池比注满乙水池所需时间多5个小时，则注满丙水池的三分之二需要多少个小时．
<gadget id="calculator">10 - 4</gadget>
<output>6</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">6 * (2/3)</gadget>
<output>4</output>

<result>4</result>