A project can be completed by A alone for 18 days, and then by B alone for 8 days; if A and B work together, they can be completed in 12 days. Now A works alone for 6 days, and then B continues to complete the rest of the project , how many days does B need to do it.
一项工程先由甲单独做18天，再由乙接着单独做8天可以完成；若甲乙二人合作，12天可以完成，现甲先单独做6天，然后由乙接着做完余下的工程，则乙需要做多少天．
<gadget id="calculator">12 - 8</gadget>
<output>4</output>

<gadget id="calculator">4 + 12</gadget>
<output>16</output>

<result>16</result>