The distance between A and B is 1890 meters. Xiao Zhang and Xiao Li start from A to B at the same time at a speed of 75 meters per minute and 60 meters per minute. At the same time, Xiao Wang starts from B to A at a speed of 90 meters per minute. How many minutes after Wang set off, is he exactly in the middle of Xiao Zhang and Xiao Li?
甲乙两地相距1890米，小张和小李以每分75米和60米的速度同时从甲地向乙地出发，同时小王以每分钟90米的速度从乙地向甲地出发，小王出发多少分钟后，恰好位于小张和小李两人的中间？
<gadget id="calculator">75 / 2</gadget>
<output>75/2 = around 37.5</output>

<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<gadget id="calculator">90 - 30</gadget>
<output>60</output>

<gadget id="calculator">(75/2) + 60 + 60</gadget>
<output>315/2 = around 157.5</output>

<gadget id="calculator">1_890 / (315/2)</gadget>
<output>12</output>

<result>12</result>