A, B, and C are three people. A walks 80 meters per minute, B walks 50 meters per minute, and C walks 100 meters per minute. A and B start from A, and C start from B at the same time, and C and A meet after 20 minutes. After C and A meet, how many minutes later, C and B meet.
甲、乙、丙三人，甲每分钟走80米，乙每分钟走50米，丙每分钟走100米．甲、乙两人从A地出发，丙从B地同时相向出发，经20分钟丙与甲相遇．丙与甲相遇后，再过多少分钟，丙与乙相遇．
<gadget id="calculator">100 + 80</gadget>
<output>180</output>

<gadget id="calculator">100 + 50</gadget>
<output>150</output>

<gadget id="calculator">20 / 150</gadget>
<output>2/15 = around 0.133333</output>

<gadget id="calculator">180 * (2/15)</gadget>
<output>24</output>

<gadget id="calculator">24 - 20</gadget>
<output>4</output>

<result>4</result>