Xiao Ming and his father went for a walk along the same road. Xiao Ming walked slowly, 60 meters per minute, so he started from home first, and after 5 minutes, his father chased Xiao Ming at a speed of 80 meters per minute. After how many minutes can catch up with Xiao Ming.
小明和爸爸沿同一条公路去散步，小明走得慢，每分钟走60米，所以他先从家出发，5分钟后，爸爸以每分钟80米得速度去追小明．经过多少分钟可以追上小明．
<gadget id="calculator">300 / 20</gadget>
<output>15</output>

<result>15</result>