Two cars, A and B, start from A to B at the same time. A travels 90 kilometers per hour, and B travels 70 kilometers per hour. Car A returns immediately after arriving at point B, and is expected to meet car B at a distance of 15 kilometers from point B, but there is no sign of car B. The driver of car A contacted by phone while moving forward, and learned that the driver of car B forgot that his things were in place A, so he returned to place A to pick up his things after starting for a while and then set off for place B. As a result, car A was 15 kilometers away from place A. Met a car. May I ask how far the driver of car B traveled before he realized that he forgot his things at place A?
甲、乙两车同时从A地出发去B地，甲每小时行90千米，乙每小时行70千米．甲车到达B地后立即返回，预计在距离B地15千米的地方与乙车相遇，但是不见乙车的踪影．甲车司机一边前进一边通过电话联系，得知乙车司机忘了东西在A地，所以出发一段时间后又返回A地取东西再向B地出发，结果甲车在距离A地15千米处遇到了乙车．请问乙车司机走了多远才发现东西忘在A地了？
<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">30 / 20</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">90 * (3/2)</gadget>
<output>135</output>

<gadget id="calculator">135 - 15</gadget>
<output>120</output>

<gadget id="calculator">120 - 15</gadget>
<output>105</output>

<gadget id="calculator">120 + 105</gadget>
<output>225</output>

<gadget id="calculator">225 / 90</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">70 * (5/2)</gadget>
<output>175</output>

<gadget id="calculator">175 - 15</gadget>
<output>160</output>

<gadget id="calculator">160 / 2</gadget>
<output>80</output>

<result>80</result>