Two engineering teams jointly opened a tunnel, each digging from one end to the middle at the same time. The first team excavated 42 meters per month, and the second team excavated 45 meters per month. After 8 months, they just dug through. How many meters is this tunnel?
两个工程队合开一条隧道，入各从一端同时向中间开凿．第一队每月开凿42米，第二队每月开凿45米，经过8个月正好凿通．这条隧道长多少米？
<gadget id="calculator">42 + 45</gadget>
<output>87</output>

<gadget id="calculator">87 * 8</gadget>
<output>696</output>

<result>696</result>