Engineer Zhang was picked up by the driver from his home to the factory on time at 8 o'clock every morning. One day, Engineer Zhang went out at 7:00 in the morning and started to walk to the factory. On the way, he met a car picking him up, so he got in the car and finished the rest of the journey, arriving at the factory 20 minutes earlier. On this day, Engineer Zhang still went out at 7 in the morning, but 15 minutes later he found that he hadn’t brought something with him, so he went home to pick it up, and then met a car that picked him up on the road, how many minutes earlier than usual this time? ．
张工程师每天早上8点准时被司机从家接到厂里．一天，张工程师早上7点就出了门，开始步行去厂里，在路上遇到了接他的汽车，于是，他就上车行完了剩下的路程，到厂时提前20分钟．这天，张工程师还是早上7点出门，但15分钟后他发现有东西没有带，于是回家去取，再出门后在路上遇到了接他的汽车，那么这次他比平常要提前多少分钟．
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<gadget id="calculator">5 / 6</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">15 * 2 * (5/6)</gadget>
<output>25</output>

<gadget id="calculator">30 - 25</gadget>
<output>5</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<result>10</result>