The distance between Xiao Ming and Xiao Gang's house is 1640 meters. The two started from their homes and walked towards each other. Xiao Ming walked 75 meters per minute, and Xiao Gang walked 80 meters per minute. If Xiao Gang left for 5 minutes before Xiao Ming started from home, how long did Xiao Gang leave when we met? (solution with equation)
小明和小刚家相距1640米，两人各自从家出发，相向而行，小明每分走75米，小刚每分走80米．如果小刚先走5分后小明才从家出发，问相遇时小刚走了多少时间？(用方程解答)
<gadget id="calculator">5 * 80</gadget>
<output>400</output>

<gadget id="calculator">1_640 - 400</gadget>
<output>1_240</output>

<gadget id="calculator">75 + 80</gadget>
<output>155</output>

<gadget id="calculator">1_240 / 155</gadget>
<output>8</output>

<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<result>13</result>