Every morning, Xiao Gang leaves home regularly to go to school on foot, and Uncle Zhang also regularly leaves home for a walk. They walk towards each other and meet on the way on time. One day, Xiao Gang went out early, so he met Uncle Zhang 7 minutes earlier than usual. It is known that Xiao Gang's walking speed is 70 meters per minute, and Uncle Zhang's walking speed is 40 meters per minute, so how many minutes earlier than usual that Xiao Gang went out this day.
每天早晨，小刚定时离家步行上学，张大爷也定时出家门散步，他们相向而行，并且准时在途中相遇．有一天，小刚提早出门，因此比平时早7分钟与张大爷相遇．已知小刚步行速度是每分钟70米，张大爷步行速度是每分钟40米，那么这一天小刚比平时早出门多少分钟．
<gadget id="calculator">70 / 40</gadget>
<output>7/4 = around 1.75</output>

<gadget id="calculator">1 / (7/4)</gadget>
<output>4/7 = around 0.571429</output>

<gadget id="calculator">7 * (4/7)</gadget>
<output>4</output>

<gadget id="calculator">4 + 7</gadget>
<output>11</output>

<result>11</result>