A and B jointly complete the task of producing 400 parts. A produces 26 pieces per hour, and B produces 30 pieces per hour. The two work together for 5 hours. A leaves for something, and B will complete the remaining tasks. How much time does B have to work to complete the task?
甲乙两人共同完成生产400个零件的任务．甲每小时生产26个，乙每小时生产30个，两人共同工作了5小时，甲有事离开，剩下的任务由乙完成，乙还要工作多少时间完成任务？
<gadget id="calculator">26 + 30</gadget>
<output>56</output>

<gadget id="calculator">56 * 5</gadget>
<output>280</output>

<gadget id="calculator">400 - 280</gadget>
<output>120</output>

<gadget id="calculator">120 / 30</gadget>
<output>4</output>

<result>4</result>