Xiao Wang and Lao Zhang each have the same number of parts to process. When Xiao Wang made 3 parts, Lao Zhang made 4 parts. According to this work efficiency, when Lao Zhang completes the task, Xiao Wang still has 60 parts left to be processed. Lao Zhang and Xiao Wang finished Xiao Wang's remaining 60 parts together, and it took 30 minutes. How many minutes does it take Lao Zhang to complete his task?
小王和老张各要加工的零件数相同，小王做了3个时，老张做了4个，照这样的工作效率，当老张完成任务时，小王还剩60个未做．老张和小王一起把小王剩下的60个零件做完，用了30分钟．老张完成自己的任务用多少分钟．
<gadget id="calculator">60 * 4</gadget>
<output>240</output>

<gadget id="calculator">8 / 7</gadget>
<output>8/7 = around 1.142857</output>

<gadget id="calculator">240 / (8/7)</gadget>
<output>210</output>

<result>210</result>