Ship A departs from a pier at an average speed of 16 kilometers per hour. After 3 hours, ship B also departs from the same pier in the same direction, and after 12 hours catches up with ship A. Find the speed of the ship B.
甲轮船以每小时平均16千米的速度从一码头出发，经过3小时，乙轮船也由同一码头按照同一方向出发，再经过12小时追上甲轮船．求乙轮船的速度．
<gadget id="calculator">3 / 12</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">16 * (1/4)</gadget>
<output>4</output>

<gadget id="calculator">4 + 16</gadget>
<output>20</output>

<result>20</result>